It is kind of a no brainer, you know the truck, it has a new/new used transmission, may have a HG issue may not, shouldn't cost much to fix, less than $500 to replace w/used engine or rebuild(providing you do the work yourself.

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed