For anyone else who happens to be doing development for these really old systems, CodeWarrior's application glue (the stuff between double clicking and when main() is entered) unconditionally calls StripAddress on the pointer to your code resource before jumping into it. These older systems don't support StripAddress, so you get an unimplemented trap even before entering your own code.

THINK C 5 generates code that works. I'm using System 3.3 (the appletalk one!) for testing on the 512k's.