vibration, engine or clutch?

does the vibration go away under load?

 

The damper does not really do anything until you get to higher RPM's, below 1800 they do very little. If in good shape, I take it, that it is a viscous damper, take it off and bounce it about 3 inches on the tire if it rattles it is junk, It could be the problem at low RPM if it is dry. If it is rubber mounted do the marks line up.
The clutch, I have added an extra lock washer on two bolts if turning the assembly does not help. You can quickly R&R bolts and see if it helps or hurts, there are only eight bolts, I would do the two on one leg first if it gets better in one section try spitting one one each close leg, of the preasure plate.
I take it you have cut apart the oil filter and checked the oil pan drain plug for particles. Done a valve set? Checked the motor mounts, good rubbers and no pieces jammed between the halves
Lots of little things can give you a vibration
It could be they did not grind the flywheel properly, and is out of balance.
Just a thought!

 

The vibration damper is held on with 6 bolts, and torqued to 150 to 170 ft lbs, you put the brakes on and the trans in high gear, using a 15/16 socket loosen the bolts then remove the damper. Two people is a lot easier to lift it out.. When you put it back on leave the belts off and run it without the belts just to be sure, it is not an accessory problem.
Before you start it be sure it is out of gear.
When working on anything I always, before I start it go threw a list, Oil, Air, Power Steering, turning devices. Works for me.

 

replace the engine damper and just for kicks a balancer from PittsPow my two cents

 

Wow I'm late