Reply to "Hall Caliper Kit..."

Hmmmm- a simple disassembly, cleaning & reassembly is normally all thats necessary to recondition Pantera calipers, and all vendors including the owner of this website stocks rebuild kits. But OK- I'm not sure on this, since Gary seldom consults me when he changes things in his catalogue.... But his 'kits' used to use Corvette or Z-28 Camaro calipers, which have MUCH larger pistons than the stock Girlings in your Pantera. He also offers several types of brake-improvement sets. You don't specify- are you using a stock Pantera master cylinder? Because, to displace enough fluid to make those big pistons move, the pedal travel will increase markedly.
IMHO, the stock non-adjustable proportioning valve and the brake pad thickness warning valve under the booster are utterly useless when calipers are changed like this. They should be completely removed for safety's sake.
As for the rigging he uses for his adaption, if it doesn't leak & is torqued tightly, a plug is a plug, even if it used to be a bolt. Not sure, but I suspect if one used bone-stock Chev calipers (assuming they really are still Chev), the stock entry connection would approach or touch some part of the Pantera front suspension, which is disaster waiting to happen. I'd call Gary directly & voice your concerns to the actual designer of this adaption.