I don't see you needing a kit per se. The only used parts your need are the spindles, caliper adapters, and upper control arm. Everything else you can order.
Here's the parts lists and how to ID large rotor caliper adapters:
http://www.moparaction.com/tech/archive/disc-main.html
One thing nice about that stock Mopar setup is that if you want to upgrade to 11.75 disk rotors all you need is a $60-80 11.75 used caliper adapter (or find one in the junk yard). You'll have to run 15" rims with that rotor size.
I just checked
www.rockauto.com and got some prices on the new stuff...
11.75" Rotors: $60 each new
inner,outer bearings & seal: $18/side new
Spindles with sheilds and 10.75 caliper adapters: $150-$200 pr for 73-76 A-body and $100-$150 for FMJ-body used
Calipers: $45-$60 each with pads $60 w/semi metalic pad new rebuilt
11.75 caliper adapters: $60-$100 used
caliper hoses: $60-100 pr braided new, $25 pr rubber new
disk master: $65 new rebuilt
adjustable proportioning valve: $45 (Mancini) new
I come up with $661 for all that. Minus $50+ if you use FMJ spindles. Minus $100 if you use $10.75 disks
For an A-body you will need some used upper control arms and new lower ball joints.
Here's a stock kit for 10.75 rotors without upper control arms:
http://shop.primoclassics.com/category.sc?categoryId=2 Wonder if you could have the substitute 11.75 rotors. They aren't very much more money. Then you'd just have to find some used 11.75 caliper adapters.