I see...what's wrong with calling buffer.resize(360,600); ? It's not meant to be used for that, but it actually does what i think you want. It limits the viewport to (0,0)-(360,600) and adjusts yFov accordingly.
BTW: I've checked board permissions...the old board (once imported from phpBB) seemed to have different permissions than the new ones (which were all set to "default"). I've set them all to "default" now. Maybe that fixes the problem with the image upload.