63Custom - I have an El Camino with that same rear end in it, same gears and all. I can tell you that during the short time the vehicle was running it made a trip down I-95 real nice. I can't tell you the exact mileage but it was upper teens with a 283 I broke in on the way to Florida. I got a couple of real good stories out of that trip.
The Chevelle rear end is a triangulated 4 bar set up with coil springs, I believe your truck uses trailing arms with panhard bar and coils. Ask any hot rodder and they'll tell you that where there is a will, there is a way. Yes you could probably put the Chevelle rear in your truck but I don't think it is as easy as bolting on the trailing arms. You want to go take a bunch of measurements starting with the relative location of the lower trailing arm mounts on each rear end. To prevent binding when using your trailing arms the Chevelle rear must have the lower mounts the same distance apart as the current truck rear end. Bushing size could be your next issue, need to measure those also. You can attach the panhard bar to one of the "ears" on the Chevelle rear but they are angled so you will need to fabricate something to allow the bar to work correctly. Its purpose is to prevent lateral motion between the body (frame) and the rear while still allowing up and down movement. Fabricating a new cross member to hold the Chevelle's upper triangulating bars may be a better answer although harder than the panhard bar.
You also need to be prepared for the 5 lug car pattern on the Chevelle rear being different than the 6 lug on the truck's front end.
Finally, you did not mention what motor you are running but if it is a 6 the 3.08 gear may be too much for the motor. Can't give you good advice on that but others here seem to think either a 3.42 or 3.73 works good for the 6; a 3.08 is best left for a V-8. Good luck
