http://www.graflex.org/helpboard/viewtopic.php?t=6333 for 4x5 lens board measurements.
http://www.graflex.org/helpboard/viewtopic.php?t=6351 for 2x3 lens board measurements
Lens board for the Pacemaker are stamped aluminum.
Go to your local hobby and crafts store and get a piece of 1/4 inch thick baltic birch plywood.
Cut the outside dimensions and round the corners so that the board will just sit into the board opening.
Remove the focus panel and insert the blank into the front standard. Mark the back side of the board for the bellows opening.
Mark the board center, both sides.
Cut the outside of the bellows opening off to the depth necessary to allow the board to just sit into the front standard with the lens board locks just clearing the front surface of the lens board.
Drill the mount hole for the shuttered or barrel lens you plan to mount.
Paint the back of the board flat black.
Finish the front side as you wish.
Substitute 1/4 inch thick black acrylic for the plywood, sand the back side so that it is no longer shinny before mounting the lens.
Having a portion of the board, usually 5/32 inch, fit inside the bellows opening of the front standard provides a sufficient light trap so that the thin outer edge lip is not necessary.
OR
watch ebay, check KEH, or Pacific Rim Camera.