Below are a few modifications to the truck I have done. As far as appearance I have removed the side mirrors and replaced the stock rally wheels.
Disc brake conversion is very simple on this model truck. The way I did my conversion was using a 1976 donor truck. The parts I used off the '76 was the spindles, rotors, steering center link, steering box, brake booster assembly, front brake lines & hoses, and the proportioning valve. On the later model booster I had to drill two new holes on the mount and drill a new hole on the break pedal for proper linkage. You could also find a disc booster for a 69 to 72 and it should bolt right in with no modification to the booster or pedal. You can use the '76 tie rods and ball joints if you want, but I purchased all new parts for my conversion. Buy your parts for a 1976 Chevy 1/2 of course. Also when getting a front end alignment, mention it's a '76 front end. On my conversion I also went from 6 bolt pattern wheels to the common 5 on 5 pattern. As you can see from the picture below, the front wheels stick out more then the rear. One reason is I used 10 inch wide wheels, but I also believe that the wheels are farther apart on the later models. I measured the rear end on my 67 and that of a 70+, and the 70+ is 3 inches wider. 1970 used the 3" wider rear end, 5 on 5 pattern, and still used trailing arms. This is the rear end of choice to change to 5 on 5 pattern and move the wheels outward, like the front.
If you want to convert to disc and keep your 6 bolt pattern, 1969 is the year to find. 69 had 6 bolt with disc from the factory. I'm not sure if the tie rods are different from 67 to 69, check with parts store, it may be easier on some years the others.
I have read that a lot of people change the entire front saddle on the truck. This is an option too. I already had new A arm bushings installed so I wanted to keep them.
Good luck on your disc conversion, any questions feel free to email me! firstname.lastname@example.org
Racing at Ozark International Raceway 11.57 @ 88.94 Mph 1000ft.
First Engine I built for my pickup, solid cam 355.