help......getting really annoyed

I bought a used engine for my '89 GT i saw the engine run before i bought it. the engine is out of a '87 GT everything looks the same i'm getting spark and fuel to the engine but it will not fire. I've gone over vaccuum lines, changed the wiring harness, checked grounds, and swapped the intake because of a difference in the throttle position sensor. all the things i tried are because that it was a thought that the stuff on that engine might not work with mine any ideas i could really use the help. did try it with that equipment though

Timing? Make a slight adjustment, then try starting.
Have you looked at the spark plugs after you tried starting? Are they wet?

r u sure u have the spark pattern the right way. it it is turning over but not starting thats what i would check.

Crank it over while spraying starting fluid in the intake. If it fires then you have a fuel problem. If it does not fire then there is maybe a timing problem. (Which could include out of time cam shafts). Is the flywheel back on? My car won't run without it because the crankshaft position sensor doesn't pick up anything. Can the fuel lines be hooked up backward? Is the fuel pump running?