Fluid Dampener How To.........???

Definetly sounds like you have a unbalance problem if it's shaking like that. You mentioned it is rebuilt but it wasn't balanced. Were the pistons changed? If so that could be the problem. If you change the pistons out for lighter ones (like so many new ones are) you will create an unballanced situation that can only be resolved by balancing the engine. No balancer you put on it will take care of that problem. The engine will need to be disassembled and balanced.

As far as which dampener to use you need to know if the engine is internally or externally balanced. Internal balanced ones were the older steel crank 340's. External balanced are the newer cast crank 340's. I'm not positive on the year they changed but I think 72 is when they went to the cast crank. If you have an older one (71 or older) it will be neutral balanced so you don't want weights on the converter and you want a neutral balanced balancer.

BTW: does the vibration happen all the time or only when your driving down the road? If it does it driving down the road only it could be a drivetrain problem such as the wrong converter, out of balance driveshaft, tire out of balance, etc... If it does do it setting still it is probably an unbalanced situation in the engine. But the one thing that is common in both neutral and driving is the converter so make sure it is correct. I would highly advise against driving it until it's resolved or it could do permanent damage.