They are a copy of the lugged, unitized USMC M40A1 mount made by a guy in Cali, plus he also made the repro Simrad mount issued to MEU units. I picked it up a few years ago and have a spare for my next build. Not sure if he's making any more though. One of his repro mounts is on a M40A1 at the USMC museum at Quantico. If ever in D.C take a drive out there it's an awesome museum!
Sorry for the dark photo but that's it in post #48 photo with the Simrad mount. It has to be fitted to a clip slotted or lug slotted action.