What aircraft are these guys in?

I believe the extra beam guns where supplied by the troops being carried.

It would be a bummer if it turned out to be a plain old He 111, and not something more exotic. I did not think the interior 111's fuselage had as finished a look as it does here, but the "cutout" in the bulkhead behind one of the beam gunners does match the confirmed picture of the He 111 interior.

Perhaps having the two picture together...seems to confirm what Graeme said.