So right now your drum car has the small upper ball joints and upper control arms. It doesn't matter what size drums your car has, since this kit will include a set of new 73+ disk brake spindles. Everything from the spindles out will be new, as well as the lower ball joints. You will need upper ball joint adaptors because the disk spindles use the larger, later upper ball joint. Your other option would be to use a set of large ball joint upper control arms. But that can be done later too, as you'll have the spindles either way. So you picked the right option there to get the adaptors, lower ball joints and bolts.
You did pick the 5x4.5" bolt pattern though, it looks like DoctorDiff only offers the 5x4" pattern in plain rotors. Although I'm sure you could call and ask.
I would suggest getting a new master cylinder since you'll be going to disk/drums. Your current master cylinder will have equal sized reservoirs , the disk master cylinders have a larger reservoir for the disks. The drum master cylinders should also have a residual pressure valve that has to be defeated to run disks, as the residual pressure valve for the drums can cause the disks to drag if not removed.
I would also suggest adding either a disk/drum combination valve or an adjustable prop valve of some kind. Your drum/drum system just has a distribution block, it routes line pressure equally to the back and front. The combination valve delays the rear brakes a touch, so they don't lock up before the disks.
Most of the stuff is pretty straight forward to replace, if you have a decent selection of sockets and wrenches up to 15/16" you should be able to handle it. If you don't have a pickle fork to break the taper loose between the ball joints and spindles you can rent those from a lot of auto parts stores. The master cylinder and combination valve will need some new brake lines though.
Cass (DoctorDiff) is also a great resource, he can answer a lot of questions about this as well as point out anything you may be forgetting as far as parts to get the project done go. Although I think most of it is covered here.