71 upper control arms and disc brakes

Same UCA if you use 1964-72 disk brakes (4 piston Kelsey-Hayes), but those parts are as rare as hen's teeth today, especially the spindles. You can keep your existing spindles and UCA's if you use Scarebird's kit, which is the least expensive approach. It adds a plate to your spindle to attach parts from more common cars (Chevy & Toyota, I recall). Those calipers & rotors will likely be available for decades. Downside is you need to drill new holes in the rotors, and in every one in the future, to fit your 5 x 4" pattern. If you go to 1973+ parts, you will also need new wheels, and rear too if you don't want to carry 2 spares (or drive commando).