Ford Repair: engine overheating, haynes book, spring side

Question
Recently had a 7.5L remanufactured engine put into a 1981 ford econline 350 rv. (previous engine was also 7.5L) Has been running hot since the mechanics changed the engine. They didnt put a new thermostat in so I replaced it myself. (spring side down) (the old one was stuck closed by a test in a boiling pot) 4 occasions of driving it stayed in normal range. 5th time driving, all the way hot (in less than 20 miles). I changed the thermostat again today thinking it might be a faulty new one. But it got hot again immediately. I havent bled the system because I cant find the bleed screws. Not online or in the haynes book. Can that be my problem? The water pump and all hoses were new with the engine change.

I cant bring it back to mechanic who changed the engine because they are 250 miles away.

thanks for your help

Answer
Unfortunately I can't determine the severity of how hot the engine got. Telling me that the mechanic is 250 miles away is some indication, and it's bad. I am thinking that you need to have the RV towed to the garage, because the heads may need to be looked at.