I made the mods needed to put the earlier side covers on my '79, I'm not doing the engine cover though (making a custom one). I'm not sure what year these side covers came from, or if there is any difference in them. I also don't know if my '79 is much different than your '83 in this respect. But it did require a fair amount of modification to make them fit. The sheet metal 'lip' at the top of the car's side partitions needed to be significantly trimmed. The '79 has a rather wide lip and the plastic covers would not fit over it. The plastic panels also had to be trimmed along that same edge (toward the engine) to clear things. The electronic ignition stuff had to me relocated. The attachment points for the covers are on the car but need to be completed. I have not attempted to fit the gas filler neck back on (tank is still out), so I have no idea what will be involved with that. After all of that the plastic side covers really did not fit that well in my opinion, but frankly I don't know how well they fit on the earlier cars so maybe that's normal. None of it was really difficult, just a lot of on and off trial fitting and tweaking until things went together. But cutting, trimming, drilling, etc, is required...certainly not a simple bolt-on job.