Engine
 

Ok so it's only a 2.0 GL but does anyone know whether its possible to change the pistons without taking the engine out?

Welcome. Short answer is no. Long answer is that it probably just about is, but the job would be so frickin' awkward you'll spend every second of it wishing you'd just gone out and hired a hoist.

Thanks!
Listening to the engine it may be that the damage is limited to the tappets.
A similar question, is it possible to access these and replace without taking the engine out?
Any views on the cost for replacing the tappets?