yeah let me know if you come up with something, I was thinking a long piece of steel, bent at a 90 that would clamp at the top of the board, and then use the screw down system you have now to tighten it. But how to transition to the "threaded" portion of the mechanism to allow that? ...

I finally got around to putting this together today. I wound up using 5/16 carriage bolts as I drilled it pretty close to the inside edge of the angle iron, but there was just enough room for a spring to fit. Came out pretty good..Just need paint at some point and some felt. Overall it came out great and no more C-clamps!

ah got to paint for glamour shots!...I thought of another way of doing the longer(rear) clamps...just use a really long carriage bolt...replace the one that's there and extend it through the bottom of the rail. Should work...