Thanks! It’s a UTG Ruger 10/22 Commando Tactical Quad Rail System (HFSonline).
Had to shorten the top rail to accommodate the magazine and tap the breech to secure it. The lower rail is only a few inches long so had to be extended to reach the trigger assembly frame.
The riser breech from Gmac allows the barrel to be raised enough so that the barrel and tube can be used to secure the fore-end with the supplied spacers.