You're in luck, the A500(+) are quite easy to towerize, if you're handy with a solder iron, a metal drill, some metal cutters and a multimeter. You don't need a fancy keyboard adaptor, just run cables with enough wires to contain all the signals from the seven or so pins on the motherboard and mount the keyboard externally. I used a couple old VGA monitor cables (they have enough wires inside) to make a long enough keyboard cable and put the a500 keyboard in the original casing, which I cut in half to resemble an A2000 keyboard (but you keep the drive and power lights in the keyboard functional). The key to the case is finding a big enough one to mount the motherboard either horizontally or vertically. A wide pc server case would work nicely for a vertical mounting (one that has the power supply and drive bays offset so as not to interfere with the motherboard. You can build yourself an adaptor to run power from a PC AT power supply in the tower to the A500's 5 pin DIN power connector (be sure to include a grounding wire to the case). When you mount the motherboard, leave enough room to be able to fit a standard sidecar expansion device (about eight inches or so) or make yourself an 86 pin female to male adaptor (out of an old ISA female connector, some old floppy/drive cable and the sawed off male edge connector (with gold contacts) off an old PC ISA slot card. If you mount the motherboard horizontally, you can simply run all of the ports to the rear of the tower on backing plates.
