Will this vanity fit into a 42 1/8 in space between two walls? According to the specification, the base is 42 in and the counter top is 42.5 in and made of cultured marble. Although the top is larger than my available space, I'm wondering if the walls, which are made of dry wall, will compress enough to accommodate the top.
I suppose you could cut a channel into the drywall, if you actually have room to get the top lined up to shove in.
Unless you've arranged some fiendish hydrualic jack system that will more likely destroy the vanity top, the drywall won't compress under normal forces that won't damage your vanity top.
Depending what it's made of (not going to go read an ad for the thing to try and sort that out if you can't just tell us) you might be able to cut half an inch off the top, though. Well, you almost certainly can cut half an inch off the top, but some materials cut more easily and with less specialized tooling than others.
I'd suggest buying one that fits.
Cultured marble can be cut with a diamond tile blade.
I have done it a number of times and it is easier than ripping out or trying to cut grooves in the drywall.
If possible cut outside, wear eye, ear and breathing protection.
I use tape to mark the line I want to cut on. If you need 3/8 of an inch clearance, do yourself a favor and cut 1/4 off each end. Walls are rarely square and flat.