3.9 engine balance

[andygears]

I just swapped an early A904 transmission (from 1970 cuda with 318) into my 1990 Dodge Dakota and now have a vibration. Some at idle but worse at 45-55 MPH. What I need to know is: How are the 3.9 liter V-6's balanced, internally or externally? There's a lot of threads on the external balance 360's and how you need a matched converter for that motor. But how is the Magnum 6 balanced? The swap was straightforward but I had a shop create a new longer driveshaft and balance it. That could be the problem, but I would like to rule out the converter before I start screamin & hollering and look like a fool.
There seems to be a small weight (bent sheet metal welded) on the old lockup converter. Also my new (old 904) converter has a drain plug with a hex head. Could I alter the balance by replacing it with an allen head pipe plug? Could that be causing the imbalance? I've cut the flex plate cover into 2 parts so I have access to the right side. Has anyone ever manually balanced a converter, in a car, by adding the weight to a nuetral converter? I figure the crank & converter pattern is the same between motors so if I added the same weight, in the same place, it would balance it without removing the converter & transmission from the truck. Mostly, I'd like some info on how that Magnum 6 is balanced.
Thanks to all
andygears

[andygears]

No takers on the balancing in a 3.9 Magnum six??

Well, I'm a brave soul and this afternoon I tried something. I measured the weight on the old takeout converter (about 1" square X .065" thick) and carefully noted the position in relation to the non-symmetry of the converter bolt pattern. I carried the old flexplate over to the lift and found the wing on the installed flex plate that corresponded to the location of the weight. Then, I cut a piece of .75" X .085" flat bar with a 3/8 hole in it to about 1.2" long. Removed 1 converter bolt, added weight/washer and tighten'd 'er up. About 80-90% of the vibration disappeared first try. I'm gonna try a little less or more because the diameter is slightly smaller and then tack weld the weight in place. Seems like it will work. and be permanent.

Comments?

andygears