G60 engine\parts are expensive and hard to find nowadays, given the price and frequency of charger rebuilds - seems like a bizarre conversion to go for given what else is available.
I'd be more interested in a slightly tuned up ABF, that could see 170-200bhp. It doesn't quite have the same charm or prestige as the G60, but is a pretty sensible option.
For big power there's the 1.8T, for the sound there's a VR6 (or supercharged

)