Seriously I would find another rolling road.
There is no way a cossie lump is going to be 207 at 1.6 bar.
The RR sounds crap, you do not EVER do a ROLLING ROAD TUNE with out AFR, never ever, this is THE most critical aspect that has to be watched.
It's a bit like going to the dentist and he has no tools so is going to use a hammer and chisel, would that be ok sir!!
If the turbo was producing 1.6 bar then it is healthy turbo wise.
You CANNOT tune or even check and engine SAFELY without AFR.
This is the FIRST thing that needs to change, before anything else.
As for any turbo upgrade see what happens with the original one first, 1.6 bar with DECENT AFR will give power aplenty for a kit car.
You could upgrade if so wished but, I would go T3 modified with T34 compressor wheel and standard T3 housing, keep the .48 turbine housing, if you make it laggy it will just be more inclined to spin when hitting boost due to light weight.
tabetha