There are LOTS of things that can contribute to overheating. One thing you mentioned was no thermo (if I understood correctly). You need a thermo to slow the flow of coolant. Even if it's gutted, just having a smaller hole to pass thru will slow the flow and allow the coolant more time to cool, while passing thru the rad.

Those electric fans may not be sucking enuff air. The fan from a Lincoln Mark VIII sucks about 5000cfm. What's the rating on yours ?

Looks like a small Holley carb. If your jets are small enuff to make it run lean, that can increase heat.

Slow timing can increase heat. Try 12-14 initial, at idle, and 34-36 total(unless that causes detonation). But 30 degrees can increase heat. You also need a good, properly functioning adjustable vacuum advance can, on your dist, hooked up to a good vac source. Most recommend hooking it directly to the intake manifold. It needs to add timing up to, but not more than your total mechanical advance. You never want your timing high enuff to cause pinging or detonation.

And if you have too much mechanical advance, you need to rig up a positive advance stop, so that you can run 12-14 degrees of initial timing, without running too much total. It is also a good idea to put at least one slightly weaker spring on your advance weights, so that all your mechanical advance will be in by about 3000rpm. or a little over.

Can't tell for sure what rad you have. But most agree that if you run an alum rad it should have 2 rows of 1" wide tubes. If it has 3 rows of narrow tubes, it will provide less cooling. And if it has 4-rows of the narrow tubes you'll need more fan power to pull enuff air thru it.

And someone usually says to make sure you have the wire spring in the lower rad hose, to keep it from sucking shut and impeding coolant flow. Well hey, that's enuff to get you started. See if any of that helps.