Yep, you were right. I've just discovered on the other side of the cylinder that it's an "A" cylinder. The other cylinder is a "B" when I was ordering the parts I assumed they were the same as I could not find a mark on it.
Nothing like assumptions, it makes an ass outta me.
So. Can I just order a new piston for an "A" cylinder or do I have to get new rings too?
Guttered.