Originally Posted by evac34
not sure what you mean by a jump box???
Originally Posted by Olblue3600
I assume you are using a jump joint to go from the 3600's drive shaft to the firebird's axle?
A conversion U-joint, one that fits the 1350 series Joint on the 3/4 ton driveshaft and the likely smaller size on the new pinion yoke.

Why not use a firebird axle? Depends on how you want to use it, it's probably not rated to hold the weight the 3/4 ton truck axle was.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-