80's roller 318. I popped the heads off and founds lots of rust in number one and two. Gaskets rusted threw. Rest of cylinders perfect. She got moisture in the front two cyls somehow. Cleaned it all up. No pitting yet. All the surfaces are good. Gonna rebuild it.So a 318 and a 340 use the same main size right? I was thinking of putting a 340 crank and rods and making a blue collar 340.Or cant it be done that way. Trying to use parts I already have.