Simple DIY serial adaptor
I didn't want to pull apart my existing connector, because then I wouldn't be able to use it with my 1-port bifferboard. So I adapted my 2-port board to have the same serial-pinout as my one-port board. Be warned that doing this means you lose the 'keyed' connection of your serial port, so you need to be careful not to plug the cable in incorrectly. Note also that all new 1-port boards have the same pinout as the 2-port boards.
If you want to do it the 'other way round' i.e. adapt your one-port board to work with the newer serial-pinout, you should be able to follow these instructions with a few simple changes.
What you need
a 4-way piece of straight pin-header
a 4-mm section of an LED 'leg' (because LEDs tend to have square legs)
a soldering iron and a some solder
Push one of the end pins all the way through, so it's only poking out of the 'short' side
Trim it to the same length as the other short-side pins
This is a bit fiddly - take the 4mm LED leg and wedge it between the pins and the plastic (it just fits!) so that the short pin is connected to the next pin. The fit is so tight it doesn't need soldering.
Use a bit of blu-tak and some folded-over paper to position your new adaptor next to the existing serial pins on your bifferboard. Be careful you don't make it too tall (as I did first time!) otherwise the lid won't sit on properly. That's why the pins are side-by-side and not on top of each other. Similarly make sure it's not too low otherwise you won't have room to fit the header on afterwards!
Dab a tiny amount of solder onto each of the three touching pins (I found it easiest to melt the solder onto the soldering iron first, and then touch it onto the pin until it 'sticks').
If you look closely you can just see the LED-leg connecting the third and fourth pins. Make sure you don't accidentally join together any of the other pins with solder.
I can now use my same serial console cable with both my old 1-port 1MB bifferboard and my new 2-port 8MB bifferboard :-)