CD-ROM should work. You'll either have to find a Windows program that will write an HFS (not HFS Extended or HFS+) CD, or the Mac should be able to read Windows CD's with these Extensions loaded: Foreign File Access, High Sierra File Access, ISO 9660 File Access. System 6 also requires the Desktop Manager extension to be loaded to mount CDs.
You'll also want a program like ResEdit on the Mac in case you have to restore File and Creator types to your archive files. Since Windows doesn't respect the Mac's hidden File and Creator types, there is a possibility that your extraction/decompression software will not recognize what type of file the archive is.