I have a 6 cyl with discs up front with 5 lugs but drums in the back with only 4. I'm wondering if I can get 5 lug drums for the 6 cyl. I know they're available for 8 cyl engines but are there any for 6 cyl...or are the 6 cyl drums and the 8 cyl drums the same?
If you've still got the 6 cylinder rear your best bet is to swap the complete rear for a V8 8" rear. Otherwise you could swap out the backing plates, and buy custom axles with 5 lug bolt patterns, but it'll cost far more than just swapping the complete rear.
oh boy! Looks like you are going to be back at square one then, considering swapping the 6 for an 8 again I mean, if you have to swap the rear still. You really don't need discs anyway, I'd go back to drums in the front, sell the disc's for some resto cash and continue to beef up the six if it were me. Of course the down side is that they have few rim options for a 4 bolt though.
To the best of my knowledge, swapping the whole rearend is the only way to get five lugs back there. Along with Pakrat's thinking: you could sell the front five lugs and then buy 4 lug disc brakes for the front (they make them for 65-66). A stock 6cylinders (drums) stopping distance is just a little longer than a v8s with discs. I would love to have discs on the front of my I6