Looking for input on my engine vibration issue.

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Hey everyone.

Once again I'm looking for input from those that know way more than me.

Problem:
347 Stroker with about 6k miles. Blueprint long block with Pro-Flo 4.
Engine dyno'd at 439hp/429tq. Started vibrating. One day it was ok, the next it was vibrating.
It vibrates throughout the RPM range, however, it is worse at about 1,700 - 1,900 and then again at 2,500, then it'll get a little better before getting progressively worse heading towards 4k.
It vibrates sitting in the driveway with the clutch in. No difference when driving.
The engine is running well otherwise.
If something worked, then it doesn't, something changed. Has to be. But what?

What I've done:
Started a warranty file with Blueprint. This is their long block.
Blueprint says it is not their long block because they can't think of anything in the long block that would make the engine vibrate.
If I push it, they'll likely take it back to test and then rebuild. I'm not wanting to do that due to the work involved and I won't see my engine back for many months most likely.
I sent my flywheel at their insistence to be checked that it is within 2gms of 28oz. If it isn't, they will make it so and send it back. (I have no use for it now)
Replaced the Energy Suspension Poly engine and transmission mounts with rubber OEM mounts. No difference and I hate them.
Replaced the flywheel from Mike Forte.
Replaced the balancer with a Fluidampr 650211.
Replaced plugs, wires, rotor and cap.
Replaced the Pro-Flo 4 ECU.
Sent pics of plugs to Blueprint and they verified looked good.
Verified timing with cylinder #1 rocker arms TDC.
Ran the engine with ONLY the balancer and flywheel - no serpentine belt. STILL VIBRATES.

Yes, I know it looks like I'm throwing parts at a problem, but some parts I already had, others were at the direction of Blueprint and some were out of sheer frustration, like the ECU, which I returned.

I am at a loss. I'm missing something. What else can I check?
I have not done a compression test recently, but I did when the engine had less than 1k on it, so I have possibly a break-in comparison. All cylinders were within 5%.

What say everyone?