1) They don't need to be exact, a difference in a few inches will make no difference.
2) You certainly can, they're just a cheap, stamped-steel frame, so knocking out any ringing isn't a bad idea. I did that with my personal pair of 600MII, and when I upgraded a pair of Spica TC60 for someone else. The woofers are pretty small compared to the RF7 III woofers, so there should be some good improvements especially for the midrange.