Yesterday I ordered a gasket kit for an Amal 376 from Union Jack Motorcycles - our carb is actually a 375, but it seems that the only difference is the bore size, making the flange gasket the only part that won't fit, and mine seems in okay order anyway. I also rang back and changed the order shortly after to include a regulator/rectifier as well, as while I could buy something similar from India for about $60 cheaper, the seller's feedback didn't exactly inspire confidence and I've seen some horror stories about such devices from asia before.
Unfortunately I also figured out that the float bowl cover for the carb is warped. I'm not sure if that's something I did (I'm usually really paranoid about over-tightening screws into alloy material, for fear of stripping the threads), or if it's been warped for a while and just me disturbing the gasket has meant that now it won't seal, but now it leaks. :(
Anyway, the package arrived this morning and I set about starting the rewire process. I soldered four different bits of new wire to the old ignition switch, then went to put it back in it's hole, and it seems there's absolutely no way I can make the damn thing fit snug. It's not an original switch for this motorcycle (the second position is spring-loaded, suggesting it's for something with an electric starter), but it is rather low-profile. The original switch (Lucas part # 31443) are rather expensive ($150AUD or so!) so it probably won't get one of those either, as cool as that would be. I had considered buying a steering lock for it (it has the socket, the lock itself is just missing) and just fitting a rotary power switch in place, but I'm not sure what to do at the moment.
I did discover while doing the wiring that the original horn does work (I'd previously found it non-functioning) which basically suggests to me that the original wiring was in worse shape than I thought. The original 6v headlamp is also not blown (though the tail light definitely is), so that wiring is probably rat-shit as well, because the switch definitely functions.