Make sure the cluster out of the C50 doesn't have a amp gauge, if so your looking at a fire. Change it out if it does, then repin the connector so everything goes where it is supposed to go. The tack will more than likely read incorrectly, here's everything showing how I fixed mine:
http://67-72chevytrucks.com/vboard/s...d.php?t=503733
Im glad you got yours fixed too bilfman!
__________________
Tony
1985 GMC K2500 restoration
Project: Rust, White & Blue
1989 Chevy R3500 CC Cummins & 4X4 swap some day...
1989 Burb (D60, 14BFF, 12V, NV4500, NP205, 37" tires in progress)