the chip will need changing to suit the turbo change or ANY other changes you make (even increasing boost). It will need at the minimum a fueling check on a wideband sensor

siemens 55lbs if you can find a set or light blue bosch or even greys if you are changing the turbo. the .48, .55 or .63 is the size of the exhaust housing on the turbo. .63 being the biggest which will produce the most power but will sacrifice later spool compared to the .48

dont take this the wrong way but you cannot afford to be slap dash with the set up of these engines, otherwise i fear you will melt your engine if you dont get it right.

has the fuel pump been re-wired? another must do for a cossie. Also you dont want to be going beyond 350/350 with your gearbox if its standard.

my old cossie was stage 3, t34.55, siemens 55lbs, msd chip, decent clutch. normal other stage 3 bits and i'd say it was around 370hp peaking at 32psi of boost