^^^^
If you only use the long block from the '89, you won't need or want all the sensors from the Renix system. All of the sensors you need will be taken off of the discarded '96. Same with the cooling system components. Double check the rotation direction of the water pumps on both engines - there may have been a change in between those years. Swapping the transfer case/tranny just complicates the job.
That said, I'm not sure the intake manifold from the '96 will work all that well with the older head. Seems like I remember the port shape changed. Do some more searching on here for info on swapping a high-output head onto an older engine - I know it has been discussed.
Personally, I would try to fix the '96 engine. If all it needs is a head gasket, it wouldn't be that hard of a job.
Edit: Whoops - I got crossed up in all of your different years. You may have a problem with the Renix system since the '96 block may or may not have a hole for the knock sensor. Since the '85 is a 2.8, you will need the tranny/transfer case from the engine you swap in. I'm not familiar with the 2.8 cooling system, but you will be ahead of the game if you can move to an open system. On a rig that old you probably need a new radiator anyway and the rest of the parts can be obtained from the boneyard for next to nothing.