ASA left side nonreciprocating upper would do it.
Take that concept one step further - the rear portion of the BCG is no longer needed for the extra mass, and that means having enough room for a short action spring to return it to battery. You can then delete the buffer or have any need for the buffer tube, ala some piston designs, allowing a folding stock.
Basically, just the upper mounted to ANY stock of choice that can hold it, with a integral 5 round mag, you now have a more typical hunting rifle with assisted straight pull.
What's the point? Aluminum receiver, barrel extension reduces weight, free floats easily, short action, top rail for mounting any scope. Using a drop in trigger and a simple mag setup, very short overall height. When you cycle the action, the bolt doesn't come back in your face, and at the end of the pull back, you just let go.
So simple a caveman can do it. . . . .