I think the lower ball joints are different from yours, one ball joint for the drum brake spindles and another for the disc brake spindles. I would do the dual line system from master brakes evn with front drums.
If I really wanted small bolt pattern disc brakes I'd go with Scarebird Mechanicals conversion kit with the option of going back to front drums if desired.
That complete KH brake system is hard to find but you'll find it even harder to find a single left or right spindle if needed. I've read about people buying mustang spindles and paying for remachining those to fit mopar rotors and bearings. Just my .02
