Vibration right off idle

What is the 42RH conversion ?

Edit:
OK looked it up on Google 42RH is a Dakota od auto trans.

Want to find out if your 340 is an internal or external balance to begin with. If it is a '70 would think that would be internal balance.

Have to see if that 42RH was set up for internal or external balance from the Dakora it came out of.