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&P...
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