Auto Parts: 1970 C20 with 8 lug rear end, leaf spring suspension, posi traction

Question
I want to replace the rear end with a Chevy 5 lug 12 bolt rear end so that I may convert to rear disc brakes with a posi-traction or locker. Or do I have to go with a 10 bolt? Any suggestions would be greatly appreciated.

Answer
    If you are going to change the bolt pattern in the rear then you need to change the front, too.  Most C20s have a leaf spring suspension in the rear; the 5-lug C10s have a coil sprung, so-called, "truck arm" suspension very similar to that used in NASCAR (in fact, that's where NASCAR got it).  The 63-72 three quarter-ton trucks (C or K 20) don't use as big an axle as the 73 and later trucks, but it is still pretty beefy.  If it was me, I'd be tempted to use an axle out of a P20 or P30 (step van).  These axles ONLY come with discs in the rear and are pretty beefy.  They would complement the C20 front axle with discs, using the same bolt pattern.  You'd want a P20 axle for single rear wheels, a P30 for a duallie.  And, you are still going to have to screw around with proportioning valves and master cylinders to get the brake balance right.