Make all the base plates you want with a laser cut plate.
If made of acrylic you can drill into it with no worries
find related projects at http://www.makeitlabs.com/ in the wiki projects
laser cut. A thick plate will need to be machined around the positive stops in the back, and the screw holes in the front. The "a" plate is the working space with the pins from the base plate and a 1" grid. Reduce the laser power to min, and go to max speed and they will be faint marks for alignment. Glue or use VHB tape. Due to stack up tolerance the plate(s) may need to surfaced or corrected with shims.