I know firsthand that CWPro 4 was the last version that could be run on 68k Macs. Pro 6 might have been the last version that could compile for 68k machines.
Trying to track down specific versions of CWPro is tricky, the updates happened every six months and I don't know how many devs held onto their old CDs. Then there was the version number confusion; the early 1997 release was "CodeWarrior 11" and the late 1997 release became "CodeWarrior Pro 1.0", resetting the version numbers in the process.
The
Classila docs recommend CodeWarrior (Pro?) 7.1 and MPW. That might be a good place to look.
Cameron Kaiser comes by these forums fairly frequently. He might know more about building the old Mozilla codebase.