New guy needs help with 85' cr250

i got the bike in a partial trade for an old truck i had, it came to me with the motor out and torn down because the piston grenaded. it has cracked piston, sleeve, metal shavings in the cases, and gouges in the crank. i would like to do the rebuild myself but i was wondering if an experienced wrench could tell me how bad this sounds. could this motor be brought back to life with a new piston and sleeve? i will be getting a manual tommorow. any help/comments are appreciated thanks