since one probably could fit sam into a genuine atx or similar case and since the board doesnt seem to be much expandable the most original idea would be to go for traditional wedge case type, while i would like to see it fitted with an original amiga style keyboard (one with the help/del keys and custom numba block). alas i do think this would be difficult to achieve.
edit: yeah the a600 was my first amiga. i bought it 4 the looks. technically it might not be state of the art but the case rocks!