I agree 100%. There is a new radiator, radiator shroud, new head gaskets (yes I know about putting them on backwards). I'm going tomorrow to the shop and look at the car and see what's on it, whats been done, and I'll take pics and post them in case you guys can see something I don't.
It is your car, I am only trying to help. IMHO, if the thermostat was unnecessary Ford would have left it out and saved the $. All you need to bypass the heater core is about 1 foot of heater hose. If you are willing to replace the engine, you should be willing to do these 2 simple things. If it is not you doing the work, then maybe the shop is the problem.
Craig if this is the case, this would be the first 289/302 out of about 10 that have ever overheated without a T-stat on me. I run my supercharged 87' 5.0 5 speed with no t-stat. In fact a couple years ago I installed a heater core in it because it was November and I was driving to Virginia to deer hunt and wanted what little heat I got to keep the windows clear. my daily driver at the time an 85' v6 I was afraid to drive that far with a bearing chattering. I'm not saying you're wrong, I'm just saying I've never experienced it. My 67' doesn't have one either because the former owner thought it was bad, when the radiator was actually plugged. I haven't put one back in it in several years yet.
I know, and I appreciate it. I'm frustrated because things people have listed are things either I or the auto shop have done already. We put new headgaskets on that was the first thing I did, the originals were on backwards, fan shroud, water pump, radiator, it DOES have a t stat (I was just at the shop), and the heater core is fine they said. They think there s a blockage in the motor itself of some kind are are going to do some kind of flush. The motor came from a friend who got sick and was dying. He put the motor together as soon as he could so I didn't get it in pieces. He died about 3 days after I got it back. It over heated. I noticed the headgaskets were on backwards. pulled the heads and replaced easy! then it just spiraled from there.
After all the things you have stated done to the engine; I believe there is some kind of restriction inside the block. Since head-gaskets were on backwards no telling what else was/is incorrect! I've driven cars w/o T-stats w/o overheating, not saying, that's true in all cases.
I've gotten blocks back frrom the machine shop that had been cooked clean but still had lots of rust and casting sand in the water jacket. Before I install the freeze plugs I turn the block so those holes are pointing downward and bop the block with a deadblow hammer. All kinds of crap comes out.
Don't run a full thermostat either. Have had to many fail. I cut the inner part out and use the rest as a restrictor. Do you know the overbore on your block. If its .060 they do tend to run hotter.
I do not see where you have confirmed that a reverse rotation water pump has not been installed. Micah
Maybe I've been lucky. In over 50 years of owning cars I've only ever had one go bad. That was 2 years ago and it had 90,000 miles on it.
Possible if the pump and pulley were both changed, a reverse rotation pump takes a pulley with the bolt holes in a different bolt circle diameter.
OK, let's go back to basics. Does it overheat mainly at idle, at speed, or no difference? I've previously read the whole thread, but I can't recall...what kind of fan does it have? Does it have a fan clutch? If it's an electric fan, what sort of electric fan? I believe you said it has a fan shroud. If not, it should. Again from memory, I think you said the radiator is new. What kind of radiator? Is it possible it needs washed out from behind? The fins can clog without it being very obvious. Are you running a vacuum advance? On the street you should. Retarded timing can cause temps to climb. You've just confirmed you have a thermostat. Presumably you've checked to make sure it's installed in the correct orientation. As the engine warms, does the upper radiator hose suddenly go from warm to hot? That's when the thermostat opens. Something else I can't recall in this 3 page thread, have you checked to see if your lower radiator hose is collapsing? Are you running antifreeze? Have you checked or replaced your pressure cap? You just confirmed you had the block tanked, and I FOR SURE wouldn't put yet another engine in without figuring out what's causing it to overheat. Likewise you've confirmed it's not the head gaskets. I promise I'm not trying to second guess you. That's a pretty comprehensive list of the things I know will cause an engine to overheat. I want to help you find "the thing" no one has thought of.
I didn't drive it around town much after I installed the engine to notice it overheating at idle. I would get on the freeway and get a couple miles down the road and steam would start blowing out of it. No fan clutch, stock fan Yes fan shroud radiator is new, shop put it in not sure what kind. Vacuum advance, yes. T stat yep and in the correct position (I surmise, they put a new one in) Radiator hoses are new with spring Pressure cap, I put a new one on the old radiator about 5 years ago. As for the new radiator, unknown. antifreeze, yes lastly correct, not the head gaskets. The shop thinks there is a partial blockage in the motor itself. They were going to flush it with I assume something high pressure. And please do second guess me, though frustrated I want to explore everything. This car has not been on the road for a very long time because of this stupid reason. It's like everyone else has said, it can only be one of a few things or so you'd think!