Glad it works for you, Spooniest! While we're retracting statements, I retract mine about Reiska not fixing the checksum. They likely did, it's just that Genesis emulation doesn't happen to like the fact that patches were mixed.
EDIT: The reason I say combining patches is the cause of the checksum becoming incorrect? I also mixed the PS: Teotm proper-caser with the level 99 bug fix, and I know for a fact that Sixfortyfive corrected the checksum for that patch as I've briefly poked around in Teotm before.
EDIT 2: I'd like to note that I would also be interested in making a version of this for Phantasy Star II's port in the Phantasy Star Collection for the GBA. I'd also like to tinker around a bit with the GBA port of Phantasy Star - as in the first of the series - and though it's in mostly ASCII so I could go do it right now, I really, really want to mess with the names of the battle commands and spells. ATTK, MAGC, HELP, PROT, TELE, TERR, WIND, and THUN all definitely, definitely need to be changed... But I don't really have the desire to do that right now.