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2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
Pretty sure you can use a diff from 64 to 77. Apparently there is strength differences if you race or manhandle them too much. The 64 to 66 had week clutch housing, and as I understand it the 69 to 70 something had a stronger case. There’s some threads on it if you want to get deep in the weeds. You’ll be fine
Mark, just do a search on the C3 TECH/PERFORMANCE Forum for GTR1999. You will find the answer to just about any question you might have regarding the rear suspension of the C2-C3 Corvettes. You may need to do a bit of reading to find the answer to a specific question, but you'll learn a lot along the way.
Gary Ramadi's (GTR1999) answers are filled with technical data and spec's so the reading is always informative. You can also send him a PM if you have difficulty finding a specific answer or are confused by a post. He's exceptionally detailed and knowledgeable regarding these cars and a great example of what makes the Corvette Forum such a terrific place to visit.