If they do the conversion Kev I would have thought it would depend on how far you go. For the basic conversion the compression ratio doesnt really alter so yes, the 2.0 lump will give you more torque at the bottom before the turbo gets going. But then who drives around at 2000 revs anyway?
If you go for the high boost, low compression version, the lowering of compression ratio will have a much greater effect than the extra 200ccs in the Willy engine, so you wont really notice the difference I wouldnt have thought. Both the 1.8 and 2.0 will run around 240-250bhp in high boost road form - having test driven this state of tune, you really dont need any more to cane everything out there. 300bhp + can be attained but only really necessary for quarter miling I would have thought.