Distribution block and adjustable prop valve

69 Valiant originally 4 drums, now 73 A body ft disc’s,rear 11 in drums.
Can I run all lines to the original distribution block then cut the line going to rear brakes on the frame rail, then install a adjustable prop valve? Or do I bypass the block and add prop valve right off master cylinder line going to rear?

Yes! Or other ways. If you want the brake warning light to work correctly then go that route.