Personally, I would look into industrial-grade i386 SBCs. Old server systems will suck juice, have non-standard weird bits and odds (old Macs are a great example for RAM) and although I readily admit to knowing next to nothing about EM shielding, it would seem easier to shield properly a small box than a sprawling monstrosity.
You can still get i386 systems at or below 200MHz from a bit of googling: http://www.advantech.gr/products/Model.asp-Category_ID=1-239XES&BU=ECG&PD=.htm or if you are feeling slightly more adventurous than i386 you might check OpenBSD/landisk or armish supported kit, although that might be a bit tight for python. anyway, hope you can find a good solution. mike
