99% of the kits are the Chevy conversion which use spindles, caliper brackets, and calipers off of a GM Dana 44. They use stock 76/77 (and later years) Bronco hubs and rotors to keep the bolt pattern correct.
The general consensus here on the board is that because the kits all utilize the parts listed above, one really isn't any different than the other. So, go with the vendor who has the cheapest overall price. With a kit this heavy, shipping is probably going to be the biggest factor in cost.