Axle Swap to upgrade to a 4.5" BP

George Jets said
Need to weld shut those 2 smaller holes on the axle flanges, machine them down flat, and then re-drill for the 4.5 studs.

but now your axle will be out of balance. the 2 small holes offset the one big hole keeping it balanced

92b said
Has any one ever welded in the original hole pattern and re-drilled at the original location? Instead of welding in the big holes.

remember all this welding on axle flange messes with the metallurgy of the steel and it is what is keeping your wheels on the car. I would opt for custom axles.