Id suggest looking at swapping the hubs, that may be the easiest route to go.
In my GMC COE I wanted to keep the old 5 lug Motor wheels which are darn near impossible to find. I upgraded to a Chevy 1953 rear axle with bendix type brakes. The old hubs fit on the newer rear, but I had to bring the drums in to a friend of mine who welded up the original 6 lug holes and then brought them to a retired machinist friend who drilled the 5 lug pattern in them.
If you have a GMC you could have any number of lugs and different hub sizes. Chevy came with the 10 lug early on and added 6 lug wheels a little later, both of which should be reasonablly easier to obtain lock ring type wheels.
Hope that helps.
Jeff
