Just an update on this, I've had some success. I revived an old Powerbook 520c that I have, which allowed me to create a 400k disk with the required software for the 512k.

I've come up with the following 400k boot disk:

System 2.0 (50k)

Finder 4.1 (47K)

MacTerminal 1.1 (98k)

BixHex 5 (8k)

- Result is around 188k free on the boot disk.

By booting the 512k with this disk, I can transfer files in BixHex format across the serial link using XModem in MacTerminal. If the files are 188k or less you can transfer them directly to the boot disk, then extract them out with resource fork in tact using BinHex to a blank 400k disk in the external drive. If the files are greater than 188k, MacTerminal allows you to eject the boot disk when receiving a file, so you can write the receive file to a blank disk. This gives you the ability to transfer a full 400k of data. Then with a bit of disk swapping you quit MacTerminal and run BinHex which also allows you to eject the program disk and extract from the data disk to a blank disk in the external drive.

So all in all, this is a complete solution for transferring files downloaded off the net directly from any Windows of Mac computer, to a Mac 512k, without using a bridge machine.

I also thought I would post my notes for wiring the serial cable, see below:

Mac db-9 Male => PC RS232 DB-9 Female - Description

7 => 6 - DSR

4 => 4 - DTR

9 => 3 - TXD

1 => 5 - GND

5 => 2 - RXD

To do some testing, I created a 512k version of MiniVMac using the actual rom from my 512k, that helped to test what versions of software would actually work. I found that many terminal programs are just too big or would not run under system 2.0. Zterm looked great but will not run in anything less that system 6.0. Screen shot of disk from vMac:

[attachment=0]MacTermBinhex.gif[/attachment]