Largest print size Jobo 4551 print drum

I just acquired a jobo 4551 print drum which is supposed to handle 50x60 prints. The Jobo label on the outside says 1 50x60 print. But the circumference is 40cm and the height is 51cms.

So how exactly is this drum supposed to do 50x60 prints? It has a 4511 format holder with it, but that doesn't seem to help. Or does it?

anyone got a 4551 drum and what dimensions are the drum diameter and height?

perhaps the question should have been: which format holder do you need to print 20x24 in the 4551 drum?