Well, You can use solvent & a scuffy pad, and clean the top of the cyls enough to use a dial caliper to see if it's already been bored over. Then pick the next oversize, but a better plan is to take it in & have it cleaned & inspected. If cracks/defects/damage is found, You'd be buying parts for an engine You won't be building, soo..... I think You have the right spirit, but once the rough bore size is decided upon, there will be no bore finishing w/o the pistons in the machinist's hands.