Help! Engine Vibration

I recently finished rebuilding and installing a 318 block with 340 heads.
It runs fine with the exception of a noticeable vibration. At idle I can observe some wobble in the vibration damper and more so at the lower pully. The vibration will increase or decrease at different RPM's.
The engine shop honed the crank and check for true. I didn't balance the assembly during the rebuild and I'm wondering if that is the problem. Other than the heads and a 4 bbl intake the motor was rebuilt stock.
The balancer is a standard replacement 318/340 balancer.

Would I be able to fix this vibration with a better harmonic balancer? What is the difference between a internal and external balancer?

The car is a daily driver my Son and I built.
Thanks
Steve, TX