Forgive me for I should know the answer to this. If my terrible memory serves me correctly the 'generation' break down by year is as follows:
(TRUCK)
79-83 1ST GEN
84-89 2ND GEN
89-94 3RD GEN

My concern is the 2nd generation. I rolled my 85 truck again and am about to do a cab swap. I've found a nice 87, and pretty sure its the same generation..but obviously solid axel vs IFS.. I figure the wiring would be the same too.. what says the PBB??

The wiring may be similar, but the connectors will be different (if that matters to you). I found very slight plug differences between the 85 body harness and the 86 battery harness (both round but have same color and number of wires, one of the plugs had changed from male to female for god knows what reason).