Hmm.. sounds like a "Stage 1" with 360deg thrust bearing and cut back blades which improves exhaust housing flow but limits maximum spool, if it is then 170bhp is a little low but not that far off normal mate!
Some will disagree with me but I and many others have never seen more than around 185bhp out of a stock turbo, and the cut back blades may limit it further.

Thats what I'd be looking at if everything else is found to be good.

From TT website..

S106 Ford Escort RS Turbo Stage 1
Power output 130-180 BHP
Boost 8-18 PSI
7° cutback turbine assembly
270° screwed thrust bearing
£415 + VAT - Buy now

Although you have a 360deg bearing this doesnt improve flow/power!