The 77-79 models are early, 80+ models are late. Yes, the 79 has serial glow plugs. It may also have a different air conditioner compressor, in a different place on the engine. It won't have an EGR, the accelerator/injection pump linkage will be different, and it has a vacuum actuated cruise control. Early automatics also had different control devices than late ones. Are you going to put the manual transmission into the good car?
BTW, there are a number of interior differences as well. Grain pattern on the dashboard, seat and headrest shape, gauges are non-metric in the early ones, slightly different climate control pattern. Can you tell I've been junkyard shopping for parts?
