I'm actually in the process of doing this. I just want to see if I can do it. I know it will be difficult. I plan on using a PIC to control the hardware. I initially thought about using a PC as the brains, but started to think about the problems with Windows (being that I'm a windows developer) not being a real time OS, so I abandoned that idea.
I have been reading over various old school pin schematics and (very) basically the components needed are a Solenoid driver board that can drive about 10 or so solenoids. I switch matrix to register the inputs. A lamp matrix to light the thing up, and the motherboard. Oh, and obviously the various components on the playfield.
I'm in the process of rigging up a test bench so I can begin development. Once all the software is written I imagine the real difficulty is the physics involved to get a good playable playfield with very little dead spots.
I figure this will be a long project, but should be fun putting it together. However, as was said by Tailgunner, would be easier to restore an older pin.