Years ago Meziere told me that my 650 HP FE needed a 55 gpm water pump to keep it cool on the street.  If you are approaching that kind of power, I think you need a higher flowing pump.  Also, a duplicate of the factory radiator in aluminum sounds like a weak spot to me, you could probably use a bigger crossflow.

A lot of people have trouble with the engine getting hot at idle, and then cooling down at speed.  This is usually the factory water pump turning too slowly at idle.  Conversely, it is also common to have decent cooling at idle but overheating going down the road; this is usually the radiator being too small, plugged up, etc.

I'm thinking that you may have both problems since you are seeing cooling issues under both conditions.  However, bear in mind that even 220 degrees is not really that hot; as long as you are not spitting coolant out of the radiator, you probably aren't hurting anything. 

Will check timing, but think it was 37 degrees all in. It runs hot at both idle and on the road. I am running a 35 gph electric water pump.
I went to an alloy radiator as it is the same size as the old copper one , but way more tubes.

Does it overheat at idle or cruising or both?  What is timing, and can you increase it without detonation?  Small water pump pulley is a good idea.

Pat

Selling components from a strong running Ford FE solid roller combination that was removed years ago and stored indoors. I originally planned to reuse these parts but decided not to rebuild the engine.

These are not stock take-off parts, these were part of a serious 428 performance engine.

- Ported FE Cylinder Heads - C7AE-A. $450 Heavily ported, 2.16 intake valves and 1.6 exhaust valves, performance springs, machined for high performance use. Has a small crack (see photos) in a head bolt boss, just in the outer edge, repairable, it doesn't extend to the deck surface or combustion area.
- Shaft Rocker System $500 Genuine Ford Power Parts (FPP) shaft-mounted roller rockers. Oiled. One rocker is a different brand but same ratio and never caused issues. They all roll smooth.
- Crower Solid Roller Lifters - $450 solid roller lifters, .875 diam. Tie-bar design,  stored oiled indoors, all roll smoothly.
- Mallory Ignition - $150 Mallory Comp 9000 distributor unilite breakerless ignition and HyFire IVA Ignition Box, unable to test but removed working.

Everything is located in San Diego, CA. I can ship anywhere in the U.S. at buyers expense.

When the weather heats up, you might try running it with the hood off or at least 1" spacers at the hinges, to make sure there is enough air flowing threw it.

Then, the first thing I would do, is put as small a pulley on the water pump, to increase the flow.

The addition of the thermostat, increasing temp, maybe says there isn't enough flow for the "that" radiator but, the fins may be to many and or to thick, not letting enough air threw.