You shouldn't need power brakes - whether or not you use disk/disk or disk/drum. I had a 454 in my A-bone sedan with disk/disk, and it worked just fine.

However, I wouldn't use a power brake master cylinder without the booster. You may not be able to generate enough pressure.

Check out the GM manual brake master cylinder on this page:

http://www.stainlesssteelbrakes.com/...Cylinder&year=