Re: Restoration of my Sonor Force 2001
David, did you consider the finish? Finishing the shells added some coating so while the coating may be pretty thin it could have added enough to make the heads not fit any more. It can't be too much of a difference though.
I'd try to gently rework just enough of the shell edges to make the heads fit. "Rework" = to just polish it gently, this might be enough.