Looks like COX ,, but what is it / go to ??

Looks like some custom bits for Cox engines that were never finished.

The backplate looks like a stock unit that was ground flat. If you figure out a way to install a NVA to that venturi tube and drill a hole in the backplate it would make for a neat custom engine.

yep, i'd guess and say a homemade backplate and a machined down 5cc babe bee tank.

I'd say Ron and Mark are on track. It does appear that it was to be some sort of custom engine, with perhaps a custom carb / venturi, spacers between "tank" back and reed valve retainer front.
Without the designer machinist to vouch, whatever it is, got lost in the primordial twilight ether.

Also wanted to add, getback, except as a display for exceptional oddly curious engine items, these days, drilling out the venturi hole in a Sure Start back (or buying one of the high performance ready-to-use from Bernie or Ex Engines) gives a lightweight NVA reed valve unit and mount.
Thus I see no technical advantage to those parts.

I also received a "custom" backplate once:



The venturi had been drilled out and a bit of a velocity stack shape could be seen too. An unknown nva was epoxied in a slot filed to the side of the venturi.

In the same pic there is an RC Bee cylinder that had had its bypasses enlarged. The guy who gave me these did not remember exactly how/if it ran, he said he did the mods in the early '80s

Some good ideas , yes i think the po was in the process of making some sort of mock up rear venture ? The back plate may work for me with setting the pilot holes for mounting the engine . I didn't think about someone turning a BB tank down Thanks Guys, if i do try and work a NVA into it i will post results