The factory rear axle in the 10 Series trucks in '64-'66, was a 12-bolt with a 3.73:1 ratio. The 4.10 was in the 3/4 ton, Series 20 truck with an 8 lug rearend.
There are many opinions on engine/tranny/axle combinations, to attain more desireable highway speeds:
Swap 4-speed transmission for automatic transmission (350 or 400)
Swap 4-speed transmission for overdrive transmission (700R4)
Higher R&P ratio rearend (3.08:1)
Swap R&P in current rearend (3.08:1)
This topic has been explored, at great lengths, on this forum. Try doing a search for a tremendous amount of information, that will identify the pros/cons to help you make your decision.
Tony Smith
