[jbclassix]

go with the DB2. what you will want to do is swap to an older harness. if you use the DB2 you will only need to supply 12V to the shut down solenoid in run/start, which carburetor equipped trucks did for the distributor. I recommend manual glow plug controls, since the gm controls can be problematic without an ECM. you will need a solenoid to handle the amperage of the glow plugs. starter and alternator wiring will be similar to carb equipped trucks. you will need to hook up the reverse light switch on the transmission, and a clutch safety switch in place of the neutral safety switch. where you'll run into needing aftermarket support I'd getting the cable driven speedo to work off the nv4500.

get the radiator out of a square diesel and use the engine oil cooler out of the 94, just upgrade the cooler hoses. if you want to use the factory gm turbo setup off the GMT400 (92-99) you will have to modify your evaporator box, but it is doable.

if you grab the harness and the little white module under the ecm out of the donor, you can make a 91 gauge cluster work for the speedo, but you'll have to do some harness connector surgery.

you're going to have to find a late square to rob the hydraulic clutch set up out of.

you're best bet with tanks is to swap to diesel tanks.