Here is a picture of the distribution block on my 68 K10 chassis should be the same for a rwd chassis I can not compare as both my rwd drum trucks have no master setup
You can see the brake light wire hanging down doyou have a block like this ?
I included a pick of my 72 c10 (blue firewall) to show the difference looks the same as my 72k10 expect where my dad added a line lock on the rear
The Distribution block will be the same power or manual brakes
The master cylinder will be different on power brakes vs manual brakes
You could look and ask on the parts board if they have one for sale
As for disc brake upgrades all depends on how you look for parts is your truck a c10 ? I have read you can use 73 87 spindles with appropriate ball joints 73 87 outer tie rods and 77 elcamino inner rods and use your center link
I have not confirmed this as i have a 72 suspension to use
One thing about 73 80 there was a light brake option available to them as well
this fact is a good read through on most options for a disc brake upgrade
http://67-72chevytrucks.com/vboard/s...d.php?t=456889