Aluminum for a rear cage/chasis? You sure you don't mean Chromoly steel? I would think 1.75" DOM would be sufficient since it sounds like you are just doing this for a trail rig, not a competition rig. I guess if you want to dump the money into 4130 Chromoly, be my guest, though i can't see any benefit for your situation. Sounds like a huge project to me. That's gonna require a lot of expensive tools and a lot of fabrication skills to do it correct.

Good Luck

-Ryan
ryan@4wdtoyota.com