http://67-72chevytrucks.com/vboard/s...d.php?t=444823
The above link is a guide for “bolt in” drum to disk using factory parts. 73-87 parts including the front crossmember bolt in. Anything newer is not a bolt in affair, requiring re-engineering and major fabrication. Think custom suspension arms or grafting in the entire front suspension.
As for the rear axle. It can be done, just buy the trailing arm axle pads and weld them to the axle of your choice. But what are you gaining? The used axle will be unknown condition and likely need brakes rebuilt, just like your current axle probably does. You said you’d like to stay drum in the rear so why change out the axle?
Brake lines. I say they’re 50 years old and should be replaced entirely. Brake fluid is hydroscopic meaning it absorbs moisture and can rot the lines from the inside out and they’re your brakes after all. But if you’re really confident in the hard lines keep em and replace all the hoses at the very least.