F,M,J Body Brakes fit on an A-Body?

I believe the lower ball joints are the same, unless your car had 9" drums. Either way, might not be a bad idea to replace them unless they've been recently replaced. You will need new bolts though, because the lower ball joints on the Diplomats were threaded, so they use shorter bolts than the A bodies.

The spindles don't need any modification. Brake hoses for a 73+ Dart with disk brakes should work fine.

And, you don't even really need to have the LBJ upper control arms. Dr. Diff sells an adaptor sleeve that allows you to use the small ball joint uppers with the disk spindles. He has them listed HERE