Further to this I've found an even better utility than BixHex 5 to transfer files across the serial link: PackIt 1.0. Packit is only 9k and allows you to archive multiple files at the source. Then at the destination it allows you to open the packit archive by simply removing the filter when opening files. Files are then restored to the destination will resource fork in tact. It doesn't provide compression, but otherwise it's a great utility.

I've done a write up of this process on my website:

http://tkc8800.com/page/File-transfer-from-pc-to-Macintosh-128k512k-via-serial-cable