going to truss my axle soon and do not want to take a chance of warping it so I am looking for ideas advice on building and using a axle jig to weld a truss onto a rear axle.This will be a simple over pumpkin square tube truss on a chrysler 8.25 rear....

A jig won't stop you from warping the tube, the only thing you can do is limit the amount of heat you put into the tube. Your best bet is to start with tacks and weld short sections allowing the tube to cool between sections. Prep it very well so you don't have to redo it and take your time.

Just to give you an idea of how I know the jig won't work, we were welding on a piece of 4" XX pipe (almost 3/4" wall thickness) that had 20 holes drilled in one side. We were welding nozzles to the holes and had the pipe secured at both ends and 2' intervals and when we released the clamps the ends each rose 3" off the table.

Take your time and good luck.

Your junk is probably already bent. If you're going to make a jig, its better to find out what way its bent and if you're lucky, the truss might help pull it in straight. I just finished up with two axles and they were both bent considerably and they came out of stock vehicles.