Tomorrow I'm bringing home a 77 3/4 ton donor truck to strip for parts for my 79 K5. The PO made sure to point out that he ordered it from the factory with the factory tach in the guage cluster (It was a very big deal to him). Anyway I was thinking that looking at a tach would be nicer than the dinner plate sized fuel guage my 79 has. What would I be getting into swapping the guage clusters? I know the 77 has a mechanical oil pressure guage but what about the rest of the wiring? I'll I need any harness from behind the dash?