Ok, I've run four different disassemblers on it, none of which gave me a complete enough disassembly to work with in a reasonable timeframe (demo...). So not much luck that route... however, with a hex editor and going by the PE file structure I have added the missing integer to the function call (but not to the code supplying it - it will remain empty - i'm hoping its optional in the new max...) and corrected the file offset created after the change all the way back to the export table; all that remains now is to correct is the portion of the import table affected by the change (location of 21 function names called from maxutil.dll, mesh.dll and MSVCRT.dll).
I'm sort of making progress, I guess. I'm not even sure this will work if I can readdress everything correctly in the dll (dli/dle) - the new TBSetCount function in maxutil.dll may not work with an integer arguement missing, or there may be further incompatibilities once all the functions imported by the plugin are found - chances are a bad function call will appear as the first error... but who knows, my hack just may work - I'll keep working on it for another week or two - after that its not much use to me because my max 6 demo will expire. Maybe Milkshape will do the job or perhaps I can get a deal on an old copy of max 5...
Edit: max reports a missing module (error 126) before it detects a missing procedure (error 127), of course, as I've just learned from testing the incompletely modified dli