first top end rebuild help

[Bulldozer]

ok so here my problem i have this 1999 suzuki king quad 300 i drove it maby 5 times since i got it i drowned it on the second ride cleaned it all out drained the oil like 5 times got it started up again drove it around the yard a few times and i fried my piston dont realy know if all that water had something to do with it but it kinda looks like it chewed up the side of the piston so i need to rebuild what i need to know now is how do i tell if its still stock piston or if its been bored out befor how do i figer out what size piston i need to buy?and how can i tell if my cam is still good and my cylinder is repairable thnx for any he

got some pics with my phone not the best sry

http://img24.imageshack.us/img24/5294/003ahp.jpg

http://img24.imageshack.us/img24/7795/004gfa.jpg