there are so many things that this could be. I would start with the basics. test using parts that you have on hand, or can borrow, or can get cheap, just to see if they work.
Usually if it overheats in traffic you do not have enough air flow.
If it overheats at highway cruise the radiator is to small or plugged up, or too little water flow.


Lack of a vacuum advance definitely will cause it to run hotter. If the cooling system is marginal, the advance will make a difference. If the cooling system is hopelessly small, the advance won't help. If you can borrow one, or test with a cheapie distributor, I would try a distributor with vacuum advance and see what difference it makes. I have a little story on this one. I did a fly-in drive home on a 68 Dodge crew cab truck. I asked the seller when I was buying the truck over the phone if I could drive it from Arizona to Minnesota. He said I don't think so, this is a 55 mph truck. I asked him if I could make the two-hour trip to my dad's house in Arizona. He said I wouldn't but maybe you could. When I got there to pick up the truck and inspect, I could see that the radiator hoses were new the fan belt was new, and the radiator had been re-cored. When I was leaving he handed me two 1 gallon jugs of water. I said has it been overheating? He said no. I said then why the water jugs? He said just in case. When I got out on the freeway, I learned that at 55 miles an hour it ran pretty warm. At 65 miles an hour it overheated pretty bad. When I got to my dad's I checked the distributor, and the diaphragm in the vacuum can was ruptured. I put in a new distributor with a new vacuum advance on it, and the truck ran cool-as-a-cucumber at any speed. So I could see that the previous owner had been trying to solve the overheating issue, but the real culprit was the vacuum advance can.
If you haven't already done so, you'll want to use a piston stop to verify top dead center on your ballancer. To make sure that the timing marks are correct so you are not inadvertently running it with retarded timing.
If you are running exhaust manifolds with a heat riser valve, make sure that that is not stuck shut. It also helps to block the heat crossover tube in the intake manifold if it has one.

You didn't say what you have for a water pump. You need a lot of flow. If you have some scrawny little drag race electric pump on there, get rid of it and put on something with a lot of flow, like a 55 GPM meziere, or a factory belt driven pump, or a flowkooler high flow. Check to make sure that your lower radiator hose is not collapsing.


Many flex fans and electric fans are useless, and some electric fans block flow on the highway. Do you see the potential problem with combining them? Try getting rid of the electric fans and put on a big 7 blade fan with a clutch. $25 at the boneyard, that's a cheap and easy test to make. See what that does for you. The next thing to look at is that AFCO radiator. It might just be too small for your application. Also if you have a high stall converter, and r using the transmission cooler in the radiator, the transmission can generate a lot of heat from slippage in the converter and actually transfer that heat into the cooling system. If this is the case you will want to use a separate transmission cooler and bypass the one in the radiator.

Good luck, let us know what you figure out, Joel