forged or cast torque converter??

crankshaft 3462387 is '72&'73 340 cast crank.

so you need the offset harmonic balancer as you already said. has to be for a 340. I'm 99.999% sure the 360's had a different balancer.

find a 340 one, test it out & cross your fingers :D

if the vibration remains -----------

on the back side, for flex plate / torque converter...

I'd get the offset weight flex plate (B&M) for externally balance engines, and then you get an unweighted torque converter (neutrally balanced). it's much easier to find a torque converter, you get many more options. since the B&M flex plate has a cutout for your weight offset, then you just buy a converter without weights, made for an internally balanced 340.

your alternative to doing that is to use what they did at the factory... just use your current flex plate and get a weighted torque converter. that will work but will just limit your choices. they also sell weight kits that you can spot weld onto a neutral balanced torque converter to make it work.