Thanks... Thats likely the problem...diffusion area etc rather than carrier size. However...i have seen some say its been done! Need to know for sure before blowing 200 quid on a useless film back.Two problems immediately spring to mind.
1. I imagine that the enlarger carrier only has a hole 6x7 in size, so some filing mght be necessary - including part of the chassis...
2. The condensers or diffusion head (whichever it is) may not cover the larger size.
I haven't looked at my Durst 6x7 enlarger to check, but I doubt it can be done.
It is a pain that enlargers for 6x9 aren't common any more.