I know that SH has quit the instrument business, but try calling or emailing their tech line
support if you haven't already. Someone there can possibly answer your questions.
As for the new square instruments and the old round holes -- most manufacturers of the new square ones have designed them so that they will just cover the old round holes. I did just that 2 years ago when I replaced some old round instruments with -- you guessed it -- some new square SH ones. I really like the instruments, and too bad they got out of that market.