What exactly is a lensboard?
Your C700 doesn't use one - it has a fixed, 39mm screw in thread.
Which means that you are a little bit more limited in lens choice than with other enlargers, which accept replaceable lensboards or lens mounts.
The 39mm thread is about as close to a standard size as you will find, so it isn't a big problem for you. That particular lens should fit perfectly.
The 105mm lens will cover a 6x9 film frame, so if your enlarger illuminated 6x9, it would be well suited to that format.
If you were to obtain an oversized, non-standard 6x9 negative carrier for your enlarger, that lens would cover as much of the image from 6x9 frames as the limited illumination of your enlarger can provide.
The longer the lens, the smaller the image on the baseboard. For that reason, the 105mm lens may limit your maximum print size on the baseboard a bit compared to a 90mm or 80mm lens (some of those were designed for 6x7 too).
To deal with print size limits, some enlargers have extra long columns or make it easy to rotate the column and print on to the floor.
FWIW, I use a 105mm lens when I want to make small prints from medium format negatives - 6x4.5, 6x6 and 6x7 - but want the convenience of a larger print to lens distance. But I have enlargers where it is very quick and easy to swap lenses - marginally quicker and easier anyways than having to screw one lens out and screw another in.
