You’re gonna need a top end kit. This will kelp you choose one that’s right for you. Some of these may no longer be available, but most are.
https://www.mopedarmy.com/wiki/Puch_cylinder_kit_summary
You’re also going to need a crank, bearings and seals. And various other accouterments. Here’s instructions:
https://www.mopedarmy.com/wiki/Rebuild_a_Puch_E50_Engine
Have fun!