I too have modified my SA-21 with great success. I paid someone $5 to do the soldering for me. Currently you can find an overview of the conversion here:
You won't have the film catch that plugs into the back of the scanner, but I've dealt with that by placing the scanner up high and allowing the film to simply hang out the back. At the end of the roll, the scanner still holds the film, so it doesn't fall on the floor.
Beats $500 for a new SA-30!