340 internal balance or not?
Sounds like you're mixing and matching parts for this engine build. That's OK. Here's some things you may know. or maybe not, about balance, cranks, and rods. 340s with a forged crank were internally balanced, 340s with a cast crank were externally balanced. (made as running change during 1972 model year). All 340 motors used HD rods. The 318 from 67 on used a cast crank and the motors were internally balanced using non-HD rods.
Easy ID for cast crank is a ΒΌ" wide casting mark in non-machined areas. On a forged crank, the mark will vary from 3/8 to 1/2 inch wide. Hope this is helpful.
