Those 3.90 gear sets are around 400 bucks I think, add to that new bearings and you got an empty wallet. Get a 14 bolt GM rear from a 73 or newer truck,they come in various ratios, full floating, semi floating, see em around for 200-300 bucks, some with posi.Takes a little fabrication work to put one in a 60-72 truck, but nothing a grinder, tape measure and welder can't take care of.
