I might be changing plans. I found this guy who is tuning his 2.5 TDI engine as we speak.

He is now up to 323 ps and 673 Nm.

Engine: 2.5 TDI PD
Original output: 174ps 350nm

Current output: 323ps 673nm

VW T5 2.5 TDI :
Flowed and ported head
Upgraded clutch
Big frontmount intercooler
Custom exhaust
Bigger nozzles
Mercedes 350CDI turbo
Custom chip