What brakes fit??

I took over a 15 year old stalled duster project from a family member and he got the 71 duster with a disc brake conversion already installed but he can't remember what the donor car was. How does a guy know so that i can order new pads when i get to that point

Does it have 4 piston calipers, if so that would be the kelsey hayes I believe which was available for 72 and before. If they are of the single piston type most likely they are from 73-up dodge, also the most common. Just ask for a set for a 73 or so dart, and there you go. Just bring in the old pads to compare. If they don't match up after that I'd take a few pics of everything and post.