340 Forged Crank Ready to Use!! OBO

Do those cranks need to be balanced to run 340 rods if in fact it is a forged 318 unit?
Yes, It should be.
Having said that, early in my career, I worked for a Moving Company, repairing their trucks, got and used a 318 stg III crank (ala rodding magazines) in a 340, - before I knew about balancing, - no vibration, no drama .
Strongly recommend balancing for anything over 500 rpm, lol.
Sorry 72 D ! !