You really need to get hold of a paper FACTORY SHOP Manual for your engine before you start the rebuilding....and frankly I would suggest you get and study it before starting to take things apart... some of the design is quirky...and even if you have done it before they often show THREE different designs for any particular component...which for instance can have a different kind of holding mechanism hidden behind it... get the manual to reduce the " Geez" factor and make this job more fun.

When you have the FSM it will tell you exactly the important GO / NO GO measurements to take ... to decide on what is needed for putting it back together properly...

There is one extra option which might save you money and still work well... except for Chas H ( who is thinking old American engine and has not seen the manual for these engines ) the above advice has been on the money as far as factory info goes...

But there are aspects of the piston land wear where you might could have a good machinist clean up the ( expensive ) piston and call the people at Deves.com
These are ring specialists and might could provide you with a deeper or wider ring to make the clearance in the cleaned up piston still meet specs... ( and save big money cmpared to those annular oil cooling ring pistons )....