brake questions for 70 gmc 3/4 ton

[wanted]

I just installed a different front end in my 70 gmc 3/4ton 4x4. I wanted disks. I purchased a new master cylinder for a 72 chevy k20. I still need a proportioning valve. I will look for a used one but what years can I use? only 71 or 72? only 3/4 ton?
Also, I would like to add power to these brakes, so I will need a booster, bracket, and different pedal assembly I assume. What I need to know, is there differences between k10 and k20 as far as pedals and booster. Also are power drum brakes set up the same. I can buy a new booster for a 72 but I'm concerned about pedal assembly and bracket.
Any help would be appreciated, I don't have alot of donor trucks to choose from up here in Minnesota.

Thanks