The engine wiring harness only has 4-5 wires to patch into the main car loom so dead easy.
The 3 door clocks will fit no bother, not 100% sure on the wiring as on the mk1 sierra there was at least 2 different car looms used, but if you're not adding the 3 door ABS ?, then all you might need would be a wire from the coil negative for the tacho, that would be the only one missing if any I would think.
afaik early sapph 2wd clocks were the same so don't pay premium money for 3 door stuff.
tabetha