Iron Pig Off Road (Lance Williams) is a TLCA member business that sells Yukons. Ihaven't heard anything bad about either Yukons or Precisions, and until Kevin's post I didn't realize there might be any difference.
As for ratio, you might simply go by tire size ratio. Stock (from the factory, 73-75 vintage) 7.50x15s bias plies were *around* 30" diameter, although a lot of them were changed out to 235R75 radials which are around 29". So 35"/30"*4.11=4.795 which is darn close to 4.88s to put it back close to factory. Of course an SBC and 700R4 isn't stock, so that's just a little perspective.