[Christ]

Are the sleeves going to go on the outside of the axle rods? If they are, the longer the axle section that fits into it, the better chance you have of them being straight.

I didn't get any measurements from you concerning them, so I can't say for sure.

2-3" should be sufficient, especially if they're close to an interference fit.

You could have had them machined so that they were a few .000's interference, then heat the sleeves before installing them, and that would pretty much guarantee that after welding, nothing would go anywhere.