When I was AR5’ing on F.3, we’d just swapped to Mk.31 LSJ with the plate on the front. IIRC there were vertical slots on the front closure plate that the mount would clip into. The AR5 manifold then slotted onto that. Happy days trapping the odd annoying crew in the airlock, decontaming the QWI junta, and watching endless re-runs of Blackadder while eating tasty tucker.