If you are going with a T5, consider a third member swap from a '55.2 to '62 1/2 ton axle. It is a bolt in to your original housing. You'll have 3.90 gears and an open drive shaft.
That is as "bolt on" as it gets for your situation.
You will still have to weld your spring pivots though.
Any other complete axle will require relocating and welding the spring pads.
