I looked again at the picture and compared to my own 40cm Novoflex with pistol grip. The setup reminds me of the oldest type of the "Schnell-schuss" systems that ended in a Leica threead, so one then would need a NIKLEI adapter (which is the one I have on my lens).
I still believe the lens head is the 280mm, as the front bezel of the 400 flares visibly out from the overall barrel.
I think it is the 300mm f/5.6 lens head, very similar to the 280mm but the tubes between focus system and lens show only the scalloped ring, not the additional knurled ring I see on the 280mm variant.
The focus system indeed appears to be the original Pi(stolen)Griff aka PiGriff aka pistol grip, not the later PiGriff systems (C and D) that use the Novoflex A mount.
