C = 6x7
To do 6x9 you have to use a 4x5 enlarger.
I think the B22 lensboard needs a retaining ring to hold the lens. If so, I would keep an eye out for a 2nd lens board. That way you don't have to deal with the retaining ring when swapping lenses on the lens board. Have one lensboard with a 50 and the other with an 80mm lens, mounted and ready to go.