Look at the top of your cylinder/head, there may be a letter stamped on it as the 82cc saws came from the factory as an "A", "B", or "C". No stamp indicates a "B".
I have a few NOS piston assemblies (piston, rings, bearings) in each size, I think Max has some as well.
I would not recommend the LRB option unless you reuse your wrist pin. I have not been happy with the LRB pistons but Maintenance Supervisor has a saw he put together with one that turned out well. LRB has ignored the three letter sizes supplied by McCulloch and offers a one size fits all.
For reference, this one is stamped "A"...
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Mark