i like that .. gonna try it, maybe with some epoxy and an aluminum rod intead of the dowel. One thing though..
I'd want to stop the piston at mid-stoke. The crank and rod angle is greater here and upward piston force will be minimal.
Near TDC when the crank/connecting rod straightens out, toggle forces will be huge.. (same goes for BDC) They make very powerful clamps based on this toggle joint idea.