1 & 2.
When you change to disc/drop spindles you can use your center link but
71-87 C20 Spindles have different size steering tie rods and ball joints than 67-70. To use your center link you will need special tie rod adjuster sleeves that allow your 67 outer tie rods to be used (in the inner position) with 71-87 outter tie rods. POL sells the tie rod sleeves part number HPAS6570.
2A. I'm not sure if the power & non-power pitman arm is the same. Might try comparing part numbers on RockAuto.
3. You will need a new master cylinder and proportioning valve designed for disc/drum combo. I used a 72 C10 master cylinder and proportioning valve on my C20 because I couldn't find the correct lines to connect a C20 master to the prop valve.
4. Most of your factory hard lines can be reused. I had to make new lines to connect the proportioning valve to the line on the frame rail.
Things to note: C20 Boosters mount to the firewall with a different size bracket than C10s. C20 boosters will not work with C10 master cylinders and vice versa. Finding a C20 booster, bracket/mount & master cylinder that all fit together was impossible. I got all my parts from auto parts stores in attempt to save money. I should have just bought a complete kit but I wanted the Willwood D52s. If you don't buy a complete disc conversion kit do yourself a favor and at least buy the booster, master cylinder & prop valve as a package.
My truck stops great with the C10 booster & master.
POL Tie rod link:
https://www.performanceonline.com/19...ONVERSIONS-Pr/