If your rearend is the original Eaton HO52 or HO72, a third member from a 1967 thru '72 Chevy/GMC C20 3/4-Ton truck will plug right in with no modifications. I installed a complete third member with 4.10 gears and the "No Slip" option in my '49 Chevy 3/4-Ton. Check out www.67-72chevytrucks.com.