[Mk2] [Turbo] Rev 3 block and Rev2 block

[royashmr2]

I always thought there were alot of difference's between the rev 3 block and the rev 2 block.
I sat them side by side to see if my rev2 head will fit my new rev3 block and they are nearly exactly the same. All i could see was a different size oil fed to the turbo.
If this is true why does every rev3 we've had go oval (bore) and smoke with piston ring probs.
I haven't got the pistons side by side to see if it them.

Any one shed any light??