250-500cc 360 Rebuild question

So... Pulled the motor apart yesterday as the bike wouldn't fire up, took the head off and the barrel was literally full of coolant (little wonder it wouldn't start). Turns out the head has a tiny hairline crack that allows a hell of a lot of coolant through!
As it's pulled down, it was suggested by my guiding hand (an uncle who's a lot handier with motors than me) that I might as well pop a new piston and rings in it. The bore looks sweet and will be fine for a while yet. This just leaves me wondering how I identify the correct size piston to order? I've taken snaps of the numbers on the barrel but I'm not sure if the bore is original etc, I'm a bit lost...a bit of help would be sweet, cheers!

The piston crown may have some info on it.
You will have to remove the carbon on top to be able to read the info.
If not measure the piston with a digital vernier.
What bike is it for?

You'll need to order a new base gasket (or make one up @1-4mm gasket paper), take the o-ring head gaskets to CBC bearings and they can size up a new set.

Pop the piston off and scrub the top which should reveal the part number and the all important letter type of the piston which identifies the bore size that came out with your 360. the OEM piston is a Wossner and it's far cheaper to buy direct than, unfortunately, the local dealer.

Part No. 8076DA - A Type
Part No. 8076DB - B Type
Part No. 8076DC - C Type
http://wossneronline.com/forged_pis...e=product_info&cPath=50_63_95&products_id=456

Like Ausky said, l would measure the piston just to see if it's tolerance and double check the size in comparison to the Wossner piston range. See my post below:
http://www.cafehusky.com/threads/piston-diagnosis.17196/#post-156823

Thanks blokes, muach appreciated. The bike is in Myrtleford at the moment, asked my uncle to throw some calipers over it and to look for some carboned up markings, hopefully I can get the ball rolling shortly

Bit of an update, she's back together after some other minor repairs, with a new piston and rings, and is angry as all hell!! I've gone through the run in procedure and she's ready to scare the pants off me.
Cheers again for the help.

Magic!!! What type wossner did ya put back into the 360?