1972 GMC Shakes at idle - where to start

[dman535]

I went through and did a full tune on our 350 GMC C10. Plugs, wires, caps, rotor, carb rebuild etc. The truck runs great, except for a shake at idle. As soon as you are off idle the shake is gone. I have popped the hood and the vibration is pretty substantial. I thought it might be a balancer, flexplate, toque convertor issue but I don't detect any driveline vibrations going down the road.

I played with timing an mixture and have it manageable but want it licked before I destroy something. I did a few open hood brake torques and the motor doesn't seem to be moving around a whole lot. I thought it might be a bad cam, but it runs to good at higher RPM to be losing a lobe.

I thought maybe my motor mounts are shot. Before I throw any parts at it - looking to get some input from the group.

Thanks

Derek.-