Adding a hard drive to the IM-403
This is actually the easiest element of the conversion. I bought a Toshiba MK1724FCV 2.5" 12mm hard drive from Westcoast Computer Parts. They are a first-rate company, with excellent prices and fast delivery; recommended.
Although I haven't tried it, it looks like you might be able to add just about any 12mm notebook hard drive to this unit. The adapter supplied by Epson for hooking up the hard drive looks like a standard notebook interface. If you try any drive other than the MK1722FCV or MK1724FCV recommended by Epson, you're on your own, though.
The IM-403 contains a slide-out bracket in the lower bay of the chassis, below the floppy disc drive bay. I undid the screw holding the bracket in place and slid out the bracket. I bolted the new hard drive into place, bolted the connector adapter in place, and slid the drive and bracket back into position. Finally, I tightened down the first screw to lock the drive in place, and my 265 MB hard drive was installed.