Robbo Jock, I asked the Bell rep at Farnborough about the chain gun on the starboard side and he pretty much dismissed it as a 'pretty' for the show. Not that it might not happen more that the mock-up was there to raise interest [like this thread!] in the project.
The reason I asked about the gun was that it was pretty obvious that it represented a significant weight and there was no counterbalancing 'lump' on the opposing corner of the craft.
I guess there might be a need for some pretty significant control inputs to counterbalance a single off centreline chain gun rattling away and of course spewing lots of little cartridge cases near the front fan!
Artistic licence by Bell!