Rob I'll start this off! You will need the whole cluster [with gauges] as the "plain" one is different than the "Gauges" one , you will also need the gauge senders, and this is where the
"UGLY" will really start. You will have to add the wiring both in the engine bay and under dash, choices being add the missing parts yourself, or find the right harnesses and swap them out You maybe able to do a combination of the two depending upon what you can find . Swapping would be the neatest, but at this point finding the harness with the right engine [4,6,or8] with, or without A/C, and headlight style [2 or 4, part of the engine harness IIRC],correct alternator size, maybe a factor(?), then the dash, I think the only significant items in play here will be Rear window defogger and A/C. You wanted to re-do the harness in fancy loom any way Right?
You may get lucky, it happens with surprising frequency with these cars. Others will chime in with what ever omissions I may have committed. Harry
I'm not a hoarder I'm a preservationist 78 Monza Spyder (~Soon(ish +/- I guess) To Be 2+2 with Spoilers)