you can install an underfolder (permanently fixed in the open position by welding/blind pinning). you will have to manufacture the rear plate that closes off the open rear on the receiver, alter the rear contour of the receiver by machining it and machining the necessary folder pivot and locking button openings in the receicer.

this is a hellova lot of work just to wind up with an inoperable folder that is far less comfortable than a fixed buttstock.

also, ace makes an adapter to install their fal type faux side-folding stock.