I was inquring the info about this enlarger a little while ago. I didn't get to have one, but there's the thread I ran:
(there was a url link here which no longer exists)
I think it can handle 6x7 at the most, but the neg carriers (especially the glass carriers) are hard to find. Also, about the light bulb, be sure you know where you can buy it. If you're in the U.S., there's a big chance for that. If not, you have to get it from somewhere.
You're right that it's (or becoming) a rare piece of equipment now. But you can still find some people who have used it before.
Good luck.