Engine shakes BADLY!!

My newly build 340 has a nasty shake/rough idle at idle.

Details of rebuild:
Balanced .40 over 340
Comp muthr thumpr camshaft
Eddy heads
Air gap
Holley 750 hp dp

All new ignition including wires and msd billet distributor

I have the timing set at 19 initial. + the lowest 18 advance in the new msd distributor

Now I've checked for vacuum leaks and can't find any. I checked the motor mounts and all good.
Firing order is correct.
I'm only pulling 5" of vacuum in park at around 850 rpm

Any ideas on why this engine runs so rough or is this just because of the cam.