I thought I'd add just one more option here. My motor bracket fits on my double rail pushpit very securely and simply. It needs to be built for the individual situation to fit, but it is very simple.
Mine is 14in. tall, 8in. wide and 2in. thick, of teak, but could be made from any wood or poly, if you can find it that thick,
the bottom is grooved about 1/2in. deep and sits on the lower rail. it is secured with a single
1/2in. stainless strap going underneath the rail and attached with a screw on both front and back. at the upper rail, the wood is grooved horizontally 1in. deep (the diameter of the rail), on the inboard side, and fits over, and flush with the rail. it extends about 1 1/2in. above the rail. It is likewise secured with a single
stainless strap going over the top of the wood and across the groove (and rail) on the inboard side of the mount. The width could be adjusted to fit the size of the motor clamps. the mount can be moved to locate anywhere on the rail, and could even be grooved to fit over the station or other vertical or angled member
of the rail. next time, I will inlet the straps so that they don't protrude beyond the face of the mount.
I wish I had a photo
to show. Its much more simple than it sounds after writing it up.