will the 83-86 f-body t5 bolt up to an 87 up engine, with the one piece rear main seal?

 

I'm sure it would if you use the '87 up flywheel. Not sure if the 2 piece RMS flywheel is different...
I do know, depending on the year of the trans, you might have no provision for the hydralic clutch on the bellhousing. Which means use the '87 up bellhousing or install a mechanical z bar linkage (hard to find nowadays). Other than that, yep it'll fit.

 

83-87 T5=NON world class, 88-92= World Class.
83-86 Flywheels=Pre 87 blocks and 87-92 flywheels with 87&up blocks.
82 and 83 Stick Cars had Cable clutches and 84 & up had hydraulic.
82 was a 4 speed not a 5 speed.
There's your differences and compatibility issues. I think thats it.

 

my car is a t5. it was converted. the engine and tranny in the car match now, and theyre a pre-87. i know that the newer trannys are world class. if it is a t5 would it be a hydraulic clutch?

 

So your car was converted to a T-5 along with a pre-87 engine. Only you can tell us what type of clutch linkage it has - Hydraulic or mechanical. If it is a 83 model, it will have a mechanical linkage. '84 to '87 will most likely have a hydraulic clutch linkage.