CHEAPest way to convert rear axle bolt pattern to big bolt pattern???

I have redrilled axles & drums on my 8 3/4 rear. I am not sure there is enough "meat" on the flange of the 7 1/4 to redrill. I will look later today.
You are incorrect about later rear assys. All 7 1/4 "A" body rears are the are width. So if you can find a later large bolt pattern "A" body rear, it is a bolt in swap. You cannot install late model LBP axles in the earlier SBP housing, the bearing size is different.