WOW, this is an OLD thread! I didn't know you could even search back that far anymore!
Since the title of this thread has nothing to do with your question, I would recommend starting a new thread with a proper title (disc brake conversion for 68 or something...)
We don't mind new threads around here
That depends on what you want to do. You can get the entire suspension from a 71/72 and it will be a straight bolt in (I mean cross member and all, it comes as one piece!) However, it will be 5 lug. You can also use a 73+ (my memory gets fuzzy on this I think you can go to 87, but I may be mistaken) but again, you'll have 5 lugs. Also, you'll want to take the entire thing again, because ball joints/tie rod ends, ect don't match up to the 68 stuff, so it's a lot easier going to the parts store and asking for everything off a 71, or 75, etc... (you can mix and match parts, but it's a pain. You'll need the ball joints for whatever year spindles you get and outer tie rod ends for those as well, it's just easier to get the whole thing.)
As far as the rotors, ECE offers them in 6 lug (I run them on my truck) but they are $, but mine are over 10 years old with 30K and look new still.
You could have a set redrilled for 6 lug.
Or you could swap the rear axle for a 71/72 5 lug rear axle, or buy new axle shafts, or have your old ones redrilled for 5 lug. You can not swap axle shafts from 67-70 6 lug and 71-72 5 lug, they are different lengths.
Crap, I just typed all the crap assuming 2wd... I have no idea what works for a 4x4.