1973 Dart Swinger Drum to disc

keep in mind wheel bolt patterns-- small bolt 5X4 and big bolt 5X4.5
you may currently have the SBP, and most disc brake kits are BBP so you'll need rims and to figure out your rear end so you don't have to carry two spares.

also, selection, sizing and price of BBP rims is much much better than SBP.

verify what you've got first and then you can plan a course of action. there are tons of options available, it just depends on what your budget is and how mechanically inclined you are.