I know. Eric White is the owner of the site and founder of their owners' club. He has amassed a lot of info about the old Columbias, but I don't know if he maintains the site anymore. From the looks of it, I'd have to say he does not.
The C-31 was only made from '65 - '68, and less than 100 hulls were produced so I know finding pictures of the interiors will be nothing short of finding a needle in a stack of needles.
From the outside, they look a lot like a C-29, but I'm not sure how that carries over to the interior.
1966 Columbia C-31
1977 Victoria 18
A copy of "Sailing For Dummies"