I feel your pain on this, I'm a long time 340 guy, and purchased a prepped 360 block ready for a stroker kit and I couldn't come to terms with putting all the externally balanced flywheels, dampner, etc. on. I used the 4.060 j.E pistons and put them in a 20 over 340 block and bought a 3.51. stroke steel crank from ma-mopar. I just protest the externally balanced shxx. I have seen too many people have the same problems you have, buy not knowing this and create a wicked vibration and wipe out there bearings.
Glad you knew enough to ask questions and figure it out, and are taking care of it.
