[Kahuna]

When I was a kid of 15, I bought an engine from a guy who was changing to a Flathead V8. The engine Vibrated quite badly at anything above an idle.
The engine cost me $110.00. My Dad loaned me 25 dollars to help me buy it
It was a B block with a Harmon & Collins cam, had adjustable lifters
Bored to 4"
Had a Counter balanced crank
Had a Burns dual intake manifold with 2 97's
Had 2 exhaust manifolds that were cut in front & welded to create dual exhaust
Had a Winfield Aluminum head
Had a B distributor
Had a 12# Aluminum flywheel. The flywheel had a steel plate that was screwed to the aluminum flywheel. This was the cause of the vibration, as the threaded holes in the flywheel were badly worn. My Dad took the flywheel to work and had some steel inserts placed in the flywheel to correct the problem for me, and then had the flywheel re balanced with the pressure plate.
As has been said by others, the only issue was low speed driveability with the light flywheel.
Jim