to run 350-400bhp you will need (if you haven't already got it)

3 bar map sensor (very unlikely you have 1 on stg1 chip)
T34 turbo (escort cosworth)
RS500 type intercooler
GRP A head gasket as bare minimum
light blues or greys

I'd go for a L8 ecu, (in fact i just have) for that to work you need a 4x4 cossie throttle position sensor, and then the outer two wires going to it need switching.

on standard cams this will see you up to around 370bhp i'd guess