Power Brakes upgrade - what is the reason for disc/disc, disc/drum & drum/drum
I've got a 1957 GMC 9300 (Chevy 1/2 ton) with 4 wheel drums. Soon, I'd like to upgrade to IFS which would include an upgrade to disc brakes. Eventually I would like to upgrde to disc brakes in back too. But for now, I want to simply upgrade to power brakes.
The power brake kits are available for Drum/Drum, Disc/Drum, and Disc/Disc applications. Why is there a difference? Is it simply the proportioning valve? or is there something else like ti will blow the brake cylinder in the drum brakes. I was going to simply order the Disc/Disc kit but am leary.
PS. I'd call them, but it's usually late and they are closed.