After speaking to Frank aka the oracle I decided to go down the corsa piston route 
Well after what seems like ages ( the bloke who deals with boring went on the sick Grrr ) I've had the newly machined block and pistons back
The machine shop wernt happy to skim the block untill I'd built the bottom end up and measured the piston to deck height.
Sooo this afternoon I built it up
Measured repeatedly and came to the measurement of 3mm to be removed ( Frank had already told me this figure but they insisted I measured )
It's all been broken down and the block is ready to go off again to get skimmed
Closer pic of piston
