In my mind, there would only be one reason to get the M1-4500...... and that would be if you were interested in trying a 4500 carb, and that was the only one way you could get it under the hood.

Probably... and not likely to happen. The car should be able to go about as fast as it's legal for with a 4150.

On the dyno you would pick up power with a Dominator but I think a Dominator would be a can of worms to sort out on your car. Spending a couple of grand to sort out a Dominator on your car seems like a waste of money. EFI would solve a lot more problems for the same investment.

The Holley web site confirms it is 3/4". And,
"The Quick Fuel Spacer Plate is required for use on the large flange 4500-style intakes with 4150 series carburetors for a smooth transition."

30 years ago I brought my home made Holley SD 4500 intake and a Dominator carb to the track and we bolted in on a friend of mines mid-10 second back half Cuda.
He’d been running an 850DP on a TM7 with an open spacer.

Same day back to back testing showed the new intake/carb combo to be worth .25 ET and almost 3mph.

Before the proliferation of aftermarket heads and stroker cranks, this scenario played out many many times.
The Weiand TR and the MP TR showed similar types of results/gains.

Granted I don’t have much experience with EFI at all, but I don’t see a $1000 Sniper EFI set up being to happy with Brads current combo.
On the other hand, the Dominator would work just fine.
It would be a 10 minute bolt on at the track if he preferred to use something else for street duty.

The Sniper XFlow should work just fine on Brad's engine. His engine would require some expert tuning since the out of the box tune isn't going to be ideal, but the tuning doesn't take more than an hour or so for an expert.

The XFlow can support up to 800 hp so it will handle his current power level without any problem. It wouldn't make as much peak power as a Dominator, but he'll improve his gas mileage on the drive back and forth to the track. Plus he would have data logging which is what he really needs.

I've used the XFlow on a couple of 700+ hp engines and it works fine. Power is down a little bit from a full race 4150 carb, but computer controlled AFR plus computer controlled timing map plus data logging is a sweet deal.

I currently run the combo using an adapter plate I fab'd up to allow a normal 4150 base plate and a 4 hole spacer. Best on the dyno was 580tq and 583hp @ 6000. I tried both the Victor 440 and the M-1 4500 and they were pretty similar throughout the RPM range. Even tried the dyno shop's HVH 4500-4150 adapter and my plate combo squeaked out a few more HP on the top end (+8HP). I stayed with the M-1 just because of it is lower height, and if I ever want to try a 4500 carb it's just a simple carb swap. Not sure how much better the TF440 is over the Victor440?

My combo is a stock stroke 440 with Eddy RPM's that came from Indy back in 2006 with the 2.19/1.88 valves. Heads had a little valve work by Dwayne in 2017 and a SFT cam spec'd by him as well. Comp is 10.5 and nothing really trick.

I actually recently swapped the RB 4500 M1 standard port intake on my 68 charger and tested at the track. The reason i did it was because i wanted to run the 1050 dominator on my car all the time and put the stock flat charger hood back on the car. It previously had a 5” six pack hood with sealed fresh air and the victor 440 intake with wilson 1-1/2” open tapered spacer for the dominator. I would consistently run 10.80-10.85 @ 126-127 mph with the victor/hood setup.
After switching to the M1 with no spacer and flat hood with no fresh air, i ran a best of 10.90 @ 125.4 mph. I was hoping it would get into the 10’s , and it surprised me with 5 of 5 runs in the 10.90’s that day. And i was missing the look of my car with the stock hood. So, for me, it was a win.

I appreciate all the feedback. I'm going to stay with the TF intake and see how my stable of 4150s works out for the foreseeable future.