Edwin,
Just my experience here.
1) When changing engine to higher CC, take note of the extra cost like road tax! Change exhaust system to 2.5 inch piping. Not to mention a change of oil every 5000 km.
2) Fuel efficiency for GSR is good. I get 400km @ RM60 (70% - 80% highway)
3) When doing transplant, make sure you visit your car everyday to ensure that they don't give you 'other' parts. Make sure they don't simply weld on the chasis (or even make unnecessary holes!). I got my car with a few extra holes ^^
4) Make sure you discuss the spart parts with the workshop, & labour cost.
5) When i changed my car, the half-cut cost 4.7k (but now, 6k liao), labour was 1.3k (terrible work), parts 1k (they insist they change all those parts!!), exhaust system 1k (big silent muffler is more expensive, expander, mid muffler,& 2.5inch pipe)...I hope you don't go into the same scenerio as I did with the workshop. Better to have everything black and white sometimes.
Remember to get a turbo timer.