I'm using a D4, which is about the same height a D2. At full height, the machine needs a bit more than 5 ft., and I have a similar low ceiling problem in the darkroom. I got around the problem by using a lower table for the enlarger, but this means that I really have to lean over to use the grain focuser. Getting fine focus with the head high up on the column is uncomfortable. Still, it works.
There have been some wide angle enlarging made, but these are expensive and rare. I've no direct knowledge of any image quality issues with these type of enlarging lenses.
For the 6x7 negatives, you'd want to look for an 80mm f/5.6 EL-Nikkor. This lens is rated to cover the 6x7 format. Similar Schneider Componon-S and Rodenstock Rodagon lenses are not rated for larger than 6x6, but my 80 mm. Schneider works fine for 6x7 at two stops down from wide open.
Checking the completed auctions for 80 mm. EL Nikkors, the prices range from $50 US and up. Prices for the harder to find 135 mm lenses are higher, but not outrageous.