I just "finished" a clamp with the holes/slot and lines... Sort of. Everything was fine until I got to the bends that hold the bubble strip/edge connector. I bent it too much, and it broke on the bend. Initially I thought I'd pitch it, but thought better. I cut off the broken bits and will use it like one of Roy's (wannawanga.com) clamp covers, so it's not total loss.
Update: I salvaged the first attempt with an "inner" clamp made of flashing. Also, I managed to fabricate two more clamps, this time without breaking anything. One was based on the template in the other Graflex thread, which proved to be a bit small to close properly around a 1.5" tube (but I've got another saber onto which that'll fit nicely). The second one is just about right. The folds to hold the card aren't perfect, but they'll do.