Easy, get an old serial A-B switch and file down the 25 pin connector to 23. Make sure the box is a break-before-make one, though - much safer!
Yes, I was thinking the same thing, a serial switcher would be fine.
Be sure it´s a fully cables one though, sometimes not all pins are used.
A VGA switchbox would also work, you would just need to make some custom cables if you monitor does not have a VGA connector (A 1940/1942/1950/1960 or 1764 all have VGA plugs, this means you would only need 2 Amiga2VGA converters, still sold new on ebay)
