Resonating vibration

This is what I know, I bought the Duster with the engine/ transmission out of the car.

The heads on the engine were built at a machine shop in Albany Ga where I bought the car.

I don't have any specs on the engine. I was told that it had a mild Comp cam in it.

Once the car was assembled it cranked right up, had a little valve clatter but that is mostly gone.

It has the Sniper2 EFI and Hyperspark ignition.

I believe all 360 magnums are externally balanced from the factory so I'm going to be checking the damper and flex plates to start.

I'm also going to have the sniper checked out because I've read some comments about it causing vibration.

I'm fairly certain it's engine related since it vibrates in neutral at idle and higher rpm's