How far do you want to go?
you would get away with charger, charger bracket, 5/6plk belt conversion and then adjust the boost return so it doesn't close completely in order to keep your boost under 1 bar. One other thing I've discovered is you can't get of the shelf maps like the turbo conversion so it would require custom mapping with any additional mod.s as you do them. Or below is where im at so far
G60 Charger
Charger bracket
5/6pk belt conversion (I've read they don't to well to toothies)
Fmic + pipe work
250kpa map sensor
Gt inlet manifold
51mm throttle body
315cc injectors
Custom map
Camshaft (I went with Schrick 276)
Exhaust system inc manifold
Head will need porting to help flow all the exta air from the g60
Wideband afr is a must
Also unless you're handy with a welder you'll need a g60 rs outlet plus inlet adapters for air filter and boost return
Sure there's more but can't think what else right now, someone will be able to point out anything I've missed.