Just my opinion, but I think you'd be better off getting an aftermarket power lock kit. Using 20+ year old vacuum equipment will not make it dependable. Many of the parts use rubber diaphrams and these can crack, dry out and rot causing various vacuum leaks (like you're experiencing already). This, plus you'll need to find an area to mount a vacuum tank you don't need with electrical units. Space on a hot rod can be at a premium! Most aftermarket lock systems cost under $200 and are universal which will save time refabricating the M-B parts to the Chevy.

Matt, just from personal experience, make a game plan to attack this project. Are locks the first thing this car needs? Plan your project by priority. Power locks and windows will not keep the car from running (unless you spend your time and money on locks instead of the engine, transmission, brakes, etc.).

Good luck!