1989 ford 302 won't run please help

I recently purchased a f-150 with 144,000 miles on it. the body was good and it had recently had alot of work done to it-rebuilt trans, fuel tanks, pumps. The previous owner hadn't run it for a couple of years due to it not running well. I took it to my mechanic who said the cats were plugged and the manifolds were cracked. I had him replace them hoping that this would cure the problem of its misfiring and not running well. That didn't help. He then started to look at the intake system in the hopes of finding a bad gasket. Bolts started to break so rather than put money into a tired engine I purchased a replacement motor out of a 94 with only 30,000 miles on it. Most everything when well in the swap but even the new motor runs rough. When new plugs are installed it will run great at about 1/4 throttle any more or any less and # 7&8 foul out and it runs rough again. Any ideas would be truely great.

Sounds like some bad injectors, get a new set. i Do beleive they are 19lb/hr.

I have changed the entire fuel rail off of a donor truck. The problem still remains.