crazy vibration

Flywheel not properly resurfaced before installing a new clutch
Worn/damaged engine or transmission mounts

Those would be the two things I would look at. If the clutch engagement was fine before engine rebuild , I would think something happened related to engine/clutch replacement.
I would question how your machine shop turned the flywheel, because some shops use brake lathes to turn flywheels and it is not an acceptable method , needs to be turned on a dedicated flywheel grinder.
Or engine /trans is moving around with load taking off and getting u-joint /driveshaft angle to the point of a vibration.
As far a oil getting on your clutch , usually that is from a rear main leaking and getting slung over time into the bell housing area, or grease being applied too heavy/incorrectly on assembly.