bigger disk brakes

Then you have a few cheap options.
1. Either find a 73-76 A-body and grab the brakes, spindles, and upper control arms.
2. Find a 5th ave, diplomat, or something like that: http://www.bigblockdart.com/techpages/spindles.shtml
3. Find an aftermarket kit, I am sure someone has the link, but the make a kit for $399 for everything