Headers certainly made a difference on my '90 with the 3.0, if you can find them chap enough and want to send the time installing them the are worth it imo. I installed mine when I rebuilt the heads(burnt exhaust valve), so I was able to drop them in from above w/the intake components removed, not sure how difficult it is with the engine complete, but I imagine it is a PITA. The crossover pipe runs under the transmission, might be an issue if you have an auto or have lowered the truck.

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