You wouldn't find any 3/4 ton parts on the early Chevy Van as the were based mainly around Chevy 2 (Nova) drivetrain parts until the '71 model year. Might be able to check the P series step van, but I think that they only had the same gearing as pickups. Also, none of my guides show a 3.73 or 3.90 in 3/4 ton. I have heard of an aftermarket 3.90, but I don't think that they are being producad currently.
