Well, after reviewing all of the really great advice, I decided on the Bell M2. I ordered it from Paula at SafeQuip, who assured me that if it did not fit, I could exchange it for the correct size with no restocking charges (Paula and Tim at SafeQuip are great to work with). Anyway, the helmet fits great, but I have another problem.

I have been wearing a Hutchens head-and-neck restraint device with my old helmet. I've been waiting for the Hans / SFI 38.1 / Isaac / Mandatory / Recommended mess to get sorted out before updating to something better, but in the meantime, I need to install the Hutchen D-rings on the M2. My old helmet was a Bieffe, and installation of the D-rings in it was easy because the liner was removable. It appears that the liner in the M2 is glued into the helmet. I have seen photos of the M2 online with D-rings installed, but can't figure out how to do it without ripping out the liner and reinstalling the liner with a hot-glue gun or something similar. Any thoughts on this dilemna?