After setting up a full software development environment in a Windows XP Virtual Machine using a combination of Visual Studio 6.0 and software from a recent AssemblerGames dump, I was able to make some progress with the SDK files.
I managed to delete the version-check code from C:\pcemu\build\charPipeline\geoPalette\src\geoPalette.c (a module used when previewing gpl geometry files).
I was then able to recompile geopalette.obj and charpipeline.lib (using the newly modified geopalette.c code) by opening C:\pcemu\build\charPipeline\win32\makeall.bat.
Once those were created, I could finally rebuild Previewer.exe and PreviewerD.exe (debug) by running the makefile located at C:\pcemu\build\demos\charPipeline\pcmakefile.
This means that the program will bypass the previous version mismatch error I was getting.
However, the program still will not actually load the model, and will crash shortly after displaying the “Loading” message.
After looking at the documentation that came with the SDK files, it seems that this issue is because the Windows version of Previewer needs gpl files exported specifically using little-endian, as opposed to big-endian (typical format for exporting for Gamecube/Mac test systems).
My best bet at this point would to continue my search for an OS 9 mac that I can run further tests on, or to find a way to convert the big-endian gpl files to little-endian for viewing on PC.