I'm in the same boat with you, so I'm curious to see what others suggest. If you wanted to swap stuff over from a later model truck to piece together your own setup but keep your crossmember and arms, you will have to change the tierods and balljoints as well.
On the other hand, there are plenty of aftermarket options available to keep your '68 stuff. From what I've found, the
ECE kit is the most complete. It has everything you need from a new master cylinder and proportioning valve down to all components at the wheel. Of course, it is the priciest of the basic disk conversion kits. Also, as far as I can tell you can only get it from ECE and they kill you on shipping.
The other popular aftermarket option is CPP, which is what I plan to do. The nice thing is you can get all their stuff through Summit for free shipping if you plan your purchases properly. The problem with their kit is it is an "at the wheel" kit, so there are several parts missing that you will need to complete it. Basically, it's missing the master cylinder, proportioning valve, and a few fittings to connect the brake lines. It also comes with flexible lines at the caliper that need to be adapted to your current hard lines. These are the things I figured I would need to complete the CPP conversion:
CPP "at the wheel" conversion kit
master cylinder
proportioning valve with bracket and lines to master
brake bleeding tool for prop valve
fitting to connect rear line to prop valve
correct brake hose from caliper to hard lines
The only thing I'm not sure of what I need is a possible adapter to go from the front hard line to the prop valve.
Keep in mind, I am still researching this like you and this is just what I've been able to gather that I need. I am fairly confident in this parts list and am ready to pull the trigger on it, but I share it here to also get some other opinions and possible corrections. I have not seen a comprehensive list of parts required for this swap so I figured we should start somewhere.