Yeah, going to need a set of T handle allen/socket wrenches. H/F Tools. Just pull the engine, to much cyld damage, and probably other problems too. Much easier to work on out of the bike. Going to need a new piston and cyld and maybe even a crank, a lot of rust, need to look inside the cases. Looks like someone modified the side main transfers.
The one in the photo is all new, Built from new cases and all new parts, ready to rock and roll. $300 shipped.
Finding a new cyld, good luck with that. It has a 37mm bore and 37mm stroke, great for rpms. I just bought 2 spare pistons at pocketbikeparts .com They were $5.95 each, a $20 piston, no ring. eBay, still has a lot of parts, search C1/C2, MT-A4 pocket bike parts. We will work with you.