Good eye! I went to check what I have and it's right about 3/4".

Untitled by Greg Ault, on Flickr

If It was mine I would try removing the existing fan and mounting plate, install a belt driven fan and test.
That alone should improve it, going down the road (but it will still heat up at low speeds due to the lack of a shroud).

I also used to use a pretty high antifreeze to water percentage (Michigan freeze protection) but went to 50/50 and
noticed a slight improvement. I'd suggest that later as well unless you're dead set against it.

A deeper shroud as mentioned should also improve it at low speeds, but if you look for one, try to find one that allows an airflow path for situations
where the car is moving 50+mph (as airflow through the grille from a car moving 50+mph is better than most any fan could provide).
Many aftermarket E-fan/shroud combinations don't have those provisions, and the fan usually ends up running constantly at higher vehicle speeds when it shouldn't be needed. In fact the fans can move slower than the air coming in through the grille, and potentially block some airflow.

Once any improvement is found, then the crossroads question is usually whether to revert to a more OE setup with belt driven fan and custom shroud, or stay with electric
and try to find a shroud with louvers or flaps that open at higher speeds and allow airflow.

I agree with removing the whole electric fan pieces, factory didn’t use that on millions of cars. Same with the aluminum radiator (are the tubes vertical or horizontal?) a friend had an all aluminum 528 Barton Hemi with same intake you got, aluminum rad with two big fans and the mezery pump, couldn’t keep it under 220. His dad had a 484 Hemi (stage 5 heads) with the cross ram and stock radiator-fan setup, ran 160 and never overheated didn’t even have a shroud.

Lots of those aftermarket electric fans don't move anywhere near the cfm they claim. Thats why a test with a belt driven, factory fan is in order.

Hard to say what the problem is until you try a few things. My guess is that those electric fans aren't pulling much air or it could be the flat plate that they are mounted on. Could also be a problem with the water pump or perhaps some other issue that is choking off the flow. As others have said I'd start by removing the fan assembly and bolting on a factory fan. See how that works and go from there.

The symptoms you are describing, almost bet its fan related.
Had nearly same issue with mine several years ago. Had a cheap, parts store fan on it and would heat up quickly on the street or the track.
Bought a GOOD fan, immediately fixed the issue.
By good, if a fan isn't pulling 20 amps or better, its motor isn't cutting the mustard. I have found Derale fans to be of excellent quality, and they are US made.
Having them on a relay(s) is also a good idea

Been working on moving the shroud back using some 3/4" aluminum angle for top and bottom and U channel for sides. Got everything done except the bottom, that will be for tomorrow. Everything has to be polished before installing, a little time consuming. Hope to test it out tomorrow when completed. Now have a full 1" between core and shroud. Hope it works. The fans were supplied by the radiator builder, he claims they are the best out there from his experience. Some guy builds them out of his garage somewhere in one of the Midwest states. The shroud has rubber flaps in bottom for high speed flow, same as used on the BeCool shrouds.

The Mercedes fan with Howie's controller is the absolute best electric fan set-up I have ever ran. Easily cooled my blown aluminum 505 Hemi in the Dart.

I don’t think I saw it posted, what are the cfm of those fans?

Forgot this, does your overflow tank have a pickup tube in side. Also I don’t see a vent hole in the tank. Under pressure antifreeze won’t go into the tank coz there isn’t air escaping the tank. If would happen to get in the tank there has to be a tube to suck it back into the rad. I drilled and installed 2 90* 1/8x barbed fittings with a clear hose to see the level of antifreeze in the tank.

Vent tube built into the bottom of overflow tank. Goes up to within 1" of top of tank to puke if necessary. Top tube go to within 1/2" of bottom to draw back up.

the overflow tank needs to be vented to atmosphere. not sure it [the vent] can be on the bottom of the tank unless it exit's the top at some point ?
i can't see that in your picture.
very nice polishing by the way !

TIMING TIMING TIMING IT WILL NEVER RUN COOL AT 28 29 DEGREES OF TIMING TOTAL my 610 cuin hemi will never run cool at 28 degrees itruns the best at the drag strip at 29 but on the street i run 35 degrees

Dump the straight antifreeze, it may have worked before on other stuff that wasn't putting as much heat into the coolant, (maybe blocks with less rust inside too, that weren't .060 over) but its thicker and doesnt dissipate heat the same. In fact I noticed my car runs 10-20 degrees cooler with straight water vs 50/50.

The fan mounting plate, as mentioned, might be an issue.

I would try a stock water pump and water pump housing if you have one and the fans/mounting plate don't make a difference.

More timing will help, some engines really run hot when you disconnect or don't run vacuum advance. I would expect that knocking it back to 28 made your problem worse.

So I moved the shroud back 3/4", bumped the timing up to 34 degrees were I usually keep it and took it for a 16 mile round trip to get gas in the tank. The temp gauge went to 205 degrees. The outside temp was 85 degrees. The first 8 miles it held at 195 running at 55mph, on the return it jumped to 205 cruising at 65 mph, sat in the driveway and let it run for about 3 minutes and the temp stayed steady at 205. Next try a water mix and move the trans cooler a little more out of the way of radiator air flow. The trans cooler has a 2" gap in front of the radiator. Can't run straight water in Michigan, during the winter the water would freeze and crack the block. Seen this many times when guys forgot to drain the block before winter weather. If someone in Michigan has a stock belt driven radiator fan I could borrow I would try that before moving on. I had the same setup on my 64 Plymouth with a 500" wedge and it never went above 180 degrees in traffic. Same water pump and housing, same size pulley set. The only difference is the brand radiator and electric fan on this car. Wedge vs Hemi both with aluminum heads.

I like at least three rows inside the radiator. The more time the coolant had sitting in the radiator the more it cools from one row to the next. One other thing I run a mated Water Pump Housing and Pump. There are a lot of differences between housing and pumps. NHOA did a study at one time and put it in there news letter on all the pumps and housings. I run a 160 high flow quick opening Stat. My set up is completely factory, 26 inch cooper rad, factory E Body completely but I do not run the clutch on the fan just the seven blade fan. I never run anything but a mixture of Anti Freeze and water like Chrysler does. 50/50. The Temp stays around 163 degrees temp taken of the pump. I don't think you want to go to what I have since you have spent money and time on making the cooling look a lot prettier than what I have. I believe you have tried all kinds of thing with the timing it can be a big contributor to a heating problem.

like others have said, ditch the plate holding the fans. I would start there. I tried that once with puller fans and it wasn't a good result. Electric fans can work, just make sure they are high flow like a spal fan. Not the chinese no name ones.