1968 442 currently with manual drum front brakes. I'd like to switch to manual front disc. I have spare disc spindles, calipers, brackets, and rotors and a manual disc master cylinder. Do I need anything else, like a different proportioning valve on the frame or hold off valve up by the master cylinder?

 

You need A proportioning valve. The distribution block you have for drum brakes has no "proportioning" function. The 1967-70 factory disc brake cars did not use a proportioning valve, they used that hold-off valve but the actual front-to-back braking balance was set with careful selection of master and wheel cylinder sizes. In your case, it's probably safer to just use an aftermarket combo valve. Also, be sure your "manual" master cylinder is no larger than 1" bore. This will ensure you have enough brake pressure for the discs. I assume you are using the 69-up single piston calipers and not the 67-68 four piston calipers.