An early Bronco with factory knuckles should have a 6 bolt spindle....
full size Ford trucks use a 5 bolt spindle.
You will need to find Chev(10 bolt or D44) or full size Cherokee/ Wagoneer (D44)spindles to do a disc brake conversion. I have heard of people using Dodge (D44) complete knuckles out for the brake conversion, but I do not know what parts or years are involved.