It is not a C700, it is a Concept Six enlarger as Bethe pointed out.
The Concept Six looks like a C700 but is really a B600 mounted on a special baseboard. This baseboard typically had a built in easel and sometimes an exposure meter and timer. The Concept Six and B600 were never meant to do 6x7 but as most of the parts are interchangable with the C700 series it amay be possible. The problem would be is the Negative Stage opening large enough for 6x7? If you really want to do 6x7 it might be a gamble and worth waiting for a true 6x7 or larger enlarger.

You may want to ask the worlds foremost expert in all things Omega, Harry at ....
http://www.classic-enlargers.com/cgi...?board=general