Can someone tell me if Im right or Wrong but I was thinking the 340 block was just a 360 bore with a 318 stroke so in theory couldn't a person just bore a 318 out to a 360 bore which im assuming would make the walls to thin so wouldnt work. Or just put a 318 crank in a 360 and have a 340? was there any other diferences on the block? Is This possible?

 

A 340 has a 0.04" larger bore than a 360 does. 340 motors also used forged cranks where the 318 motors used cast. The valves in the heads were 2.02" intake/1.60" exhaust.

You could build yourself a 340 motor but it will still have the casting numbers of a 360.