If I understand you're question, You want to make a 318 into a 340 by
boring,"drilling," it to the 340 size. Can't be done. The cylinder dia. for a 318 is 3.910, and the 340 is 4.040. You'll be into the waterjacket long before you get the 318 bored,"drilled," to the 340 size. The 273, 318, and 340 cranks will physically interchange, but they're all balanced differently
because of the different weights of the pistons etc.
