In an earlier thread I posted a picture of the new OK .049R engine with tank now here is the BR engine without a tank. Note that both of there engines have both radial and beam mounts. $34.95
Larry

(Looks like that'll make for a pretty complex radial mount. And hopefully, does the venturi rotate so the needle valve can be horizontal?  And, what kind of plug does it take?  Have any specs on performance? (I'm just full of questions today...)

Glow plug is a standard short plug
The venturi screws into the back plate of the engine Rotate, I guess.
No, I have no specs I only sell these things, I make model kits you will need to check with OK Engines.
As to mounting.....remember the bulkhead on the autogiro? There is a hole in the center, cut through the balsawood behind that hole, open up the pilots seat, extend the needle valve and you are set with a nice fit in the cowling.
Larry