I got a chance this evening to do a quick strip of the HLF variant of the ARP9. At first I was certain that they XYL and HLF used the same receiver but that’s not the case and I’ll save that for another thread. You’re here for the gearbox right. So this looks to be a badgeless warinterest box. The 2.5 or version 3 perhaps. It looks the same as the box from an LDT HK416.
The MK V2 box is a fit.
If you are in a pinch you can transfer the internals of the box into the MK V2 shell. Expect a few tight squeezes since the plastic internals aren’t exactly made to a tight tolerance.
I’d use the loom and cylinder head again.
I’d bin the trigger block piston head and piston, nozzle, selector plate.
The grip lines up perfect!
T Piece sits almost flush against the box. The barrel retainer spring needs to be stretched IMO to push it up against the box a fraction for the ultimate nozzle seal.