1970 340 Balance Problem...Bottom Line

Under the previous "Fluid Dampner, How-To" thread, there was quite a bit of great information on balancing of early Mopars, and especially the problem we have been faced with relative to our 1970 date coded 340.

To recap, our 70 340 has a vibration problem at 1400 and 2800 rpm's, whether driving or parked. We thought it was most likely a mismatch between the engine and an aftermarket torque converter......it's quite a coincidence that as I was watching Barrett-Jackson a few minutes ago, Rick from the Speed Channel was commenting on exactly that problem, which was faced by many an unsuspecting buyer as they changed their conveters over to the popular "stall" configurations.....Lots of vibration due to the mismatch of counterweights.

I wanted to draw a bottom line here, and ask all of the guys again about the specifics of this problem........

What we have is a 1970 340, with the stock crank and stock harmonic balancer. I've been told that the stock balancer will have a "counterweight", denoting the engine as externally balanced. A-Body guys...IS THIS CORRECT?

If so, what torque converter must be used on this engine? (and if it's NOT a stock replacement Mopar or equivalent, what will be the proper "name" or distinction that we must ask for when purchasing an aftermarket converter?

Bottom lines here..........Is the 1970 340 an externally or internally balanced engine? (from the factory, that is)......How do we tell from outward observation if it's externally balanced?........and due to this distinction, what type of torque converter MUST be used to avoid adverse vibration?

After researching this, I've found that it is a COMMON problem still today, and seems to be especially relative to the 1970 engines.

What are the bottom lines?

Doc