1976 Scamp fuel gauge problems

I know it's more work and money than you want to spend, BUT, the best possible way to fix that car would be to keep the 72 cluster as is, and swap out the dash harness for a 75 style one. You MAY need to change the position of some of the pins on the bulkhead connector to correspond with the underhood harnesses, so some schematic studying would be a good idea, but that 76 only stuff is very hard to find in good, working order.
I do have a perfect dash harness if you decide you want to go that way.