Looks good, Phil.
I had a similar set up with a C-clamp, but later modified mine. I made an adjustable rear block out of hardwood 2 x 4, augured a 7/8 ths (I think) hole through the block, then epoxied a long "coupling" nut into the block. I replaced the shorter threaded portion of the C-clamp with a 1-ft threaded rod so I could get a much longer travel on the business end of the compressor, my C-clamp "head room" being a bit short for one of the rifles I was working on. I put two regular nuts on the rear end, locking them together, and then just use a 3/8rh inch ratchet driver to run it in and out under a load. I managed to get the hole retaining the coupling nut crooked, but I just squared up when I drilled the vertical holes to hold the block to the base. Not very elegant, but it has worked OK so far for the few rifles of my own that I have worked on.
