A-100 have two different spindles, one for 10" brakes (2200 lbs front axle), another for 11" brakes (2500 lbs front axle).
Scarebird has done the 2200 lbs in the past.
I had the 11" brakes (2500 lbs axle).
I sent him a 2500 lbs spindle to adapt his C body kit. It bolted on fine, but then the calipers hit the bolt on steering arm that attaches to the spindle (duh, I didn't send that).
So - I moved the calipers to the front, and that required sway bar link mods.
Anyway - I was supposed to try to see if the caliper mounting bracket would be able to be clocked enough to rear mount the calipers and clear everything, but life got in the way...so I dropped the ball.
Email Scarebird, his site is not up to date.

BTW - My brakes work fine, I had to panic stop recently and they saved my behind.

I might want to experiment with MC size in the future, the calipers are really big, so they might require a bigger MC than the one I have (1 1/8" dia), but I'd rather test pressures before swapping out stuff.

If you have the 11" brakes, and no sway bar, than what he has right now can fit (front mount).
If you have 10" brakes, he has a kit.

Also ECI has a kit for 10", and possibly other B body kits can be adapted from different vendors, but not 100% sure.
AAJ Brakes also has a kit, and in the A-100 Yahoo group, Bobby V or Scottie have brackets.

So - different options, feel free to PM for more details.

Ran