We're creating a bumped-out wall with an inset fireplace (ventless, bioethanol), similar to this to give you an idea.
One notable difference however is that the bottom of the fireplace will be about 12 inches off the floor.
I framed out the wall with 2x6's, leaving a box to insert the fireplace into, only in my attempts to be as exact as possible, I didn't leave quite enough clearance to get the box in. I'm sure the box isn't exactly plumb and square, and additionally, the fireplace box itself has domed screws that stick out farther than the listed dimensions in the instruction manual.
Is there a good way to "shave" down the insides of the lumber to allow the fireplace to go in? At this point, the wall is already in-place and has been ramset-nailed into the floor, so any advice to avoid having to bring the wall down would be great.