Hi. I've recently acquired my father's fxdc after his passing in February.  

Pull cam plate and check run out. Also check to see if it's sumping. Sounds like a scissored crankshaft. If check looks ok then check main gear drive bearing. But I'm calling bullshit on harley mechanic's comment if the vibration is excessive.

There is a method to shim up the mount and settle the engine into place, without seeing it it's hard to say what's going on, BOnes could well be right if it's had a bit of a hard time, the mech is full of it, same frame except for neck rake, same engine, it's a version of the old "they all do that" line, there was a thread on here that went into it, not sure if it's still up.

Nice that you've got your dad's bike Dan. My daughter says she's gonna ride my old rat Sporty to my funeral, hopefully not too soon.

Thanks mate. Funeral was a great turn out up here in Townsville.  We had his coffin ⚰️ taken from morgue to crematorium on a motorcycle hearse. We had about 47 bikes including my brother and myself on our Harley's escort him. And about 150 people at his service.  He would of been proud as punch I reckon. 

Check clearance on rubber, shim mount, check exhaust not touching frame, check head studs