Ed - A quick swing through GM Partswiki shows your rear wheel studs should be 7-1/6" - 20 x 1-7/32". The 1/2" - 20 x 1-63/64 ones are listed as 3/4 and 1 ton truck wheels studs.
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~ Dan
1951 Chevy 3 window 3100
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"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)