If you are willing to accept using a magwell adapter in a standard AR lower, in addition to Macon Armory, Stern Defense might have what would be acceptable for you in the way of a product that provides LRBHO capability.
Another potential product is the 1911 magazine pattern 'bolt on' magwell block sold by Blind Squirrel Enterprises.
A factor to consider that you might not be aware of is that the typically suggested preferred total weight of BCG plus recoil buffer (i.e., approximately the weight of the reciprocating parts) for a non-delayed (so-called "straight") blowback AR .45 ACP configuration is approximately 25 ounces or higher. Use of a hydraulic buffer might be able to reduce the weight required somewhat.
In any case, as noted above, the Rimfire and Pistol Calibers Forum is the place to inquire.
Best of luck.
MHO, YMMV, etc.