Sharpie pre90 mk2s also had the single piece glass doors, its the pre 87 cars that got the 2 piece glass
You are correct tho, 2 piece glass & single piece glass front motors are different, but front 3 & 5 door motors are the same. Rears are all the same regardless of year though!
The wiring is the same on all MK2s, you just have to figure out where to plug in the live, ign live & earth wires, as the locations differ on pre & post 90 MK2s see my fusebox FAQ in the garage section