I am considering changing my 69 Dart from small bolt pattern drum brakes to small bolt pattern disks and have a couple of questions. Are all years of SBP disk brakes the same as far as interchangability goes? Also, when doing the swap, would I need to change the UCAs or LCAs or are the same ones used for drum and disk? Is there anything else I should know about when doing the swap?

same setup 65-72. Same LCA & I believe same UCA. Been awhile but iirc the lower ball joints are the same but you'd drill out the 2 holes from 1/2" to 9/16". There's plenty of material to safely do this & the iron is soft & takes minutes on a drill press

Robert is correct. There are some slight variations between the early and late calipers in the way the dust boots attach and the pad retainers. It doesn't matter which pad retainers you use and the later ones are available from any Mustang resto supplier. The boots cannot be interchanged and some kits only have the early boots.