Hello, Maxim! Thanks for dropping by and giving us a shout at SMS Power! SMS Power and your little corner of that website has helped me get to grips with how the Master System and its games work, so thank you, Bock, and everyone else involved.
z80dasm worked really well, so I'm definitely going to use it more often. Disassembling that part has, as expected, opened up a fairly large rabbit hole, where more Z80 instructions have been mistaken for data. Looks like I'm going to be busy tonight.
[Edit] In the meantime, here's a disassembly of the part ccexplore requested. Copy and pasting it into the source should be sufficient to make it work.