Does power brakes equal disk brakes on a 68 Barracuda?

Power brakes was a stand alone option. My guess is that if you don't have a code for discs, your car came with power drums.

Discs were optional even on the Formula S, and a fairly expensive one at that, $72.95.

That's $490.35 in todays money. Just about the only more expensive (non drive-train) option was AC at $334.60 (or $2249.09 today).