connecting rod and harmonic balancer question

I wouldn't worry about the different forging numbers. They are both 340/360 rod forgings. I WOULD spend the money to have the engine balanced, though just in case there is a weight mismatch. I can't tell from the photos of the balancer how bad the rubber is. Can you try to get a better photo of it? I noticed you're in San Jose. I'm in the SJ area, too. Where are you going to have your machine work done?

As a former machinist, I'm always on the lookout for a good machine shop.