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

According to the spec sheet I have, it's a 1970 340, stock crank, bored .30 over, LD340 Intake, Edelbrock aluminum heads, Holley 670....mated to a 727 with a shift kit, and a 2800 stall converter....................

I've been told different things by different people relative to the "crank vs. converter" problems some have experienced.

How do I know that this is the "right" converter for the motor with a steel crank, which I'm told was stock on the 1970? I had a tranny shop take a look for some obvious problems today, but that was as fruitless as I had suspected it would be..........

This motor has a leaking rear oil seal already, with less than 3000 miles on it.......no idea why....... I need to have the trans dropped and the seal replaced.........I suppose if I replace the converter with a stock model for the 1970 motor (unless you guys know of some reason I'd NEED a stall in it for driving and cruising), and then the vibration stops, I'm ahead of the game...................

BUT, if it does not stop the vibration, then I can just about be sure that it's the internals...............rods, pistons, etc..........correct?

Again, it vibrates in Park....not just driving.....it's in the engine, not the wheels or tires..........when driving, you hear and feel the constant "wom-wom-wom" of the balance problem, that changes frequency with your rpm's..............at parked idle, it's 1400 and 2800 consistently.

If it's the internals, is there a general concensus here that a dampner of some sort will NOT balance it? (Why not, I have to ask....I know it's more serious than a wheel, BUT it's the same mathematical principle, is it not?.....if the dampner won't balance it, what purpose does it serve? Race only? Super RPM's?)

Thanks for the time guys.....................Need to fully understand this if possible, before we start throwing money at the problem.

Doc :salute: