Looks like they used a different piston and modded the cylinder to work with it.

Need to verify some measurements:
1) Rod Length & part number (to ensure it's a stock rod):
2) Cylinder deck height from base surface to head surface
3) Pictures of the head

With these 3 measurements you should be able to tell what's been changed and adjust as needed.  If the cylinder has been cut down to run this shorter piston and you want to run a real LT500 piston you may be able to put a base plate in it to compensate depending on what the measurements are.

Pictures always help diagnose the issues too.