ive read these engines are notorious for this. Any help would be appreciated.

Water pump : Good
Thermostat: New
Radiator: cleaned
New Electric Fan pushing

From what I’ve read is could be losing vacuum advance from either a torn diaphragm or something loose between carb and vacuum canister. All I know is what I’ve read but information on the 223 seams to be limited. I believe it to have the loadomatic which is full vacuum advance. Is there a conversion for a fully mechanical distributor? I guess that’s my mane question. Also if any other ideas might come up. I still may be running a tad rich as well.

Runs good for a while then just loads up on heat at cruising RPM. Runs at 170 degrees or so at idle.

Thanks for all the help in advance.

 

Hey WL, welcome aboard.

Others will chime in, I'll offer some thoughts. Not knowing what you have to work with as to testing.
1- 223 yes Load-a-matic dizzy (distributor), test with timing light, see if advance. If no advance bad diaphragm OR no vacuum signal from carb. Load-a-matic dizzy must have Carb designed for it...... Test with hand held vacuum pump, engine off, dizzy cap removed, apply vacuum watch dizzy breaker plate move, this test, if OK, moves Bplate, says diaphragm is OK.
2- Over heat, engine warmed up and idling, rev the engine and watch the lower rad hose. See if it sucks itself closed, hose collapses. If so there should be a large spiral spring inside the hose to prevent collapse. No collapse, YOU SAY radiator cleaned, by you or radiator shop who verified good flow? Again engine warmed up, T-stat open, Rad cap removed (CAREFUL), rev engine and look in filler opening for a forceful flow of coolant circulation. If not good flow you may have a plugged radiator.
3- It is common for older inline sixes that have not had good cooling system maintenance to accumulate heavy rust/sediment around the cylinder walls which will cause a flow restriction and lack of heat transfer. Only good check is remove freeze out/ expansion plugs on side of block to inspect.

A bit winded, just trying to cover a lot of back and forth, Good Luck, Cap

 

I'm thinking radiator myself...