You probably figured this out by now, but I just completed this nasty little project today myself. At first I bought the wrong fan, got home and realized that our 40-year-old fan was an axial fan which mated directly to 7" round ducting, straight up, through the roof. Since access to the crawlspace would've been a huge hassle (to try and make a centrifugal fan work instead, as suggested above), I went back to Home Depot and bought an $87 NuTone axial fan (it's a "NuTone 8210 8" Vertical Discharge Utility Fan"). Although it's called an 8" fan, it actually has a 7" outlet (so it mates with 7" round ducting). The darn thing sure is loud at 6.5 somes, and very utilitarian in appearance. But it sure sucks out air at a pretty good clip: 210CFM. I actually like its utilitarian aesthetic and it works quite well with our "industrial-tech" motif, but I would've much preferred to install a quieter Panasonic fan instead (don't think they make axial-mount fans). Anyway, bought some 7" ducting, and went at it. This was a tremendous hassle, with a PITA factor of about a million. Finally got it in and wired. Anyway, the moral is . . . they do make axial fans that should be a near- direct fit to your existing cavity and ducting.

Do a drywall repair then match the texture and paint.

It looks like the bolts are in an anchor---if that is spinning, there is little hope of getting the bolt removed. You might try using a hammer to hit the bolts sideways/up/down/at all angles to loosen it in the brick. If that works, fill the holes with patching compound, smooth and paint. If that does not work, cut them off and grind them flush with the brick and patch.

I need to remove just the fan blades to clean them. There is one a screw looking thing the blades are hooked to.