Wrong sized bearings could make vibration, if you could force yourself to keep on driving despite the horrible death clatter coming from the engine. Regardless of how well balanced the internals are the flywheel or clutch pressure plate balance could be off, or missing a clutch pressure plate bolt. Or a loose driveshaft flange or u-joint can shake things around, but it's nothing that shouldn't be painfully obvious through the gear shift (BUZZZZZZZZZ!).

As for the alternator - it's possible that you are getting an alternator with a too-small pulley. If the engine is spinning at 5000 rpm and the alternator pulley is 1/2 the size of the drive pulley then the alt is spinning at 10,000 rpms (or whatever the ratio is between the two pulleys). The A/C Delco might have a pretty small pulley for use with the low(er) revving domestic engines of yore.