The exhaust studs that you want to replace (all of them really) should be replaced with those from a z31 (ZX300) of the same era... the heads will have to be drilled out and threaded for the 10mm bolts and is work but well worth the effort.
Ask about oil changes in the transmission, not the engine. Has any work been done to the trans? The factory did NOT put enough oil into the trans when they were building them so the bearings and gears get starved for oil in 4th and 5th.... if there is the least amount of noise in the tranny or difficulty getting the gear to engage, that's the end-of-life for that trans. Take $750-$1000 off the price for a rebuilt trans.
Bring a 10mm closed end wrench and pull the positive wire off of the battery and ground it (no you won't damage anything); put it back on, tighten it down and THEN get in and start the engine. If anything has been fiddled with this will re-set the capacitors and learned trouble-codes in the ECU, the TCU and oxygen sensor feedback. Take a few seconds and play with all of the knobs and buttons in the truck before taking off on the test drive. Do NOT turn the truck off before you've taken it for a test drive, you want all the trouble codes to be set before you turn it off. Make sure that you get it into top gear on the highway, feel for shaking and shimmy which are going to be symptoms of bad suspension bushings in the rear, tie-rods in the front, both or ball joints or all of the above. Back in the day this was the _best_ handling truck in it's class. if the front end is in good shape it should feel tight and light at the wheel with good feedback and sharp turn-in. Anything short of that is suspension work.
That's about all I can give you, 'cause that's all I know!