Easy job and I've done it tons of times. Just cut the centers out of the wheels the rock pattern as close to the wheel as you can. Then grind them down smooth. Then buy a cheap ass set of wheels with the bolt pattern that you want and do the same thing to them. Now take a Rockwell hub and weld a flat 1/2" plate onto the outside of the hub. Knock out the wheel studs and turn them around and re-install them going the other direction. Now take your new wheel center and bolt it to the Rockwell hub. Now take you wheel shell and slide it down over the wheel center and down onto the flat plate. make sure that the wheel is down on the plate flush and start tacking the new center to the wheel shell. Once your certain that its square then you can finish welding it. Bam..you now have a new set of centered wheels with 4" of back spacing.
I've literally done this tons and tons of times.
