Here's what info i have:
On the underside of the piston you should find two numbers, this denotes the diameter of the piston at 20degC - for example, 75 means that the piston is 86.975mm diameter, 80 would mean 86.980 etc.
This is measured 10mm above the piston skirt.
The piston to bore clearance is set at 0.020-0.030mm, this should determine the size of your hone.
Hope that helps