It has been way too long since I've used MPW to give you a definitive answer on how to fix this, but I can give you a few breadcrumbs:

Yes, it is possible to change the compilers in MPW. If you are dealing with a new version of MPW and old MacTech articles, then the compilers definitely would have changed.

From what I recall, library and include paths were passed to the program via command line options that are in the makefiles. These paths are usually passed as environment variables, so you will have to find out how to query their contents and how to change them.