The 1984 was the "odd duck" of M102 motors and bodywork. This early engine had different internals, including a shimmed valve lifter, instead of the later hydraulic lifters, a different camshaft, lower compression ratio and lower HP than the versions that followed. The newer engines will mount, but make sure you take all the auxillary pieces, like the alternator, ECU, etc. from the donor vehicle. Another key difference with the '84, but won't affect an engine swap, is that the single nozzle hood and windshield wiper are unique to the '84.