Help! Engine Vibration

Yea, I know that that it was a dumb A$$ rookie mistake. The block is dated 1980. I do have the cast number of the crank but I couldn't tell you if it is internal or external balanced.
The builder was me, my kid, and the help??? of my body guy, (a chevy man). So a lesson learned. Now, I'm just trying to figure out if I can smooth things out short of a rebuild.
All advise appreciated.