If I remember correctly there is, or was, going to be a “big block” mould which would house the larger boolits. If these are not a figment of my imagination then perhaps these could be used to have 3 (or 4?) slug cavities . . .
Regarding diameter, is it possible to orbit a .665″ (or smaller) cherry to make a 12 gauge slug. I think I remember when Mihec did his they would have been oversize for 16 gauge and I want to replace my undersized Lyman.