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If “some car experience” means you’ve personally overhauled an auto engine, the Leopard shouldn’t present too much of a problem. As Pat noted, the primary issue is splitting the crank, as the conrod on a 2-cycle is a single piece and has to be slipped on and off the crank pin. This can be fairly tricky as there are special plates required for different cranks and your local machine shop might not have the correct ones for a Leopard. You’ll probably need to have the cylinder turned/bored to the next piston size, assuming it still has some meat left. Rough guess, you’ll be looking at $500-700 for a DIY including parts and shop time, excluding tools you don’t have, and assuming the normally reusable parts are in fact reusable.
You’ll also want a circlip installation tool: http://www.italianmotorsusa.com/collections/tools-and-machines-specialty-tools/products/125cc-circlip-assembly-tool
Might be out of your price range, but this is killer deal where you trade in your leopard and get a whole new motor including radiator, wiring harness, etc.: http://www.italianmotorsusa.com/products/x125t-mx-engine