93 Cobra Rims on 89 GT

[RMARIANI]

I've asked this question before, so I hope I don't piss anybody off!! I bought a set of 93 Cobra Rims. I know I need to change my front rotors up front to get the correct offset for the rims. I still have rear drum brakes. I was given 5/8" spacers and longer studs by the guy I bought the rims from. I won't use them on the front (I'm buying the new rotors) but what about the rear? I tryed to locate a complete 93 cobra rear end, but that's been impossible. Ford doesn't sell the complete rear, but the parts guy says I could buy it in pieces, if I knew what I needed!! Any suggestions? If I go to SSBC or Baer rear discs, will that give me any additional offset room?? Thanks in advance and sorry for the long post!!