My T5 and driveshaft are from an '83 S10. The adapter came from Hot Rod Works and mounts a 1982 thru 1992 T5 to a 1937 thru 1947 bell housing. I did have to cut the driveshaft down but that's easy, just ask the driveshaft shop what measurements they need and $150 later your down the road.
I'm running a '58 1/2 ton rear end with a 3.38 gear so that's just like yours.
Don't get too worked up about your overdrive ratio unless you've modernized your front suspension and brakes. I don't find it to be a usable gear until around 60 or 65 mph which is faster than I care to drive my original suspension.

Steve


1946 1/2 ton