Front wheel backspacing w/ disc brake conversion

[PumiceMan]

I've searched the best I can in the FAQs and in this forum, but haven't quite found what I was looking for.

I've got a 69 GMC 1/2 ton longbed with manual drums all around, and 6 lug 15" wheels (I'm assuming they're 15x7?). I'm currently planning on buying a 6 lug front disc brake conversion kit with 2 1/2" drop spindles (keeping the stock height springs). I was told that my stock wheels will not fit, because they have too much backspacing (~4 1/2" on the stock wheels), and that I'd need to go to something with no more than 3 1/2" of backspacing. Is this only true for 15" wheels? Or only for stock wheels? Where does the interference occur?

If I understand correctly, the disc conversion moves the wheel mounting surfaces towards the outside of the truck (wider track). If I decrease backspacing too, they move farther still, especially if going to an 8" wheel. I was curious what kind of wheel sizes / backspacing combinations are on your front disc setups. If I am going to have to buy new wheels, I want to have some idea of backspacing required so I know what my options are. If I get aftermarket wheels, say 15-17 inches and 7 or 8 inches wide, what are my backspacing options? Likely manufacturers would be Cragar or Wheel Vintiques (classic looks).


Thanks for any info you can provide!