Bob
I believe that you may find that 3/4 ton calipers, with a larger piston, and therefore generating more clamping force, will bolt on with a tight wheel-to-caliper clearance up front. A grinder may take care of that. I haven't tried it on my 71/72, but for my 91 Sub with 10 bolt front axle, the 3/4 ton calipers are bigger and better...
I havet eh body off the Jimmy now, and some spare calipers, so if you need, I can test fit the 3/4 ton calipers pretty easily for you, using "later model" GM 15x8 rally wheels.
To get really good brakes, consider the following as well:
* Carbon-Kevlar pads (Praise Dyno Brake in Royse City TX -
www.praisedynobrake.com) - Talk to John...
* They also sell cryo-treated rotors and drums, but try the pads first - they have a MUCH higher coefficient of friction than metallic or organic pads...
* Hydroboost in place of the pitiful vacuum boost which is stock - this implies change of PS pump, MC, booster and hoses...
I'm a brake nut, so if you want to discuss this further, send me a mail.
Take care
JB
PS - are you going to dun CanBack pronto to see where their Gen1 project is?