Just completed the PID modification to my brother's Silvia as a birthday present. I am quite pleased with the results, I think it is reasonably aesthetically pleasing without requiring extensive stainless steelworking.
The PID is a 1/32DIN standard version from TC Direct. The thermocouple was sourced from Rapid Electronics (since they have a glass fibre sleeved version). PTFE cable sleeving and the SSR were purchased from RS Components and the case is available from Maplin.
Cables are routed out of the Silvia and straight into the PID box through matching holes. Neat and tidy !