Chatter while engaging the clutch is often caused by sloppy motor mounts. Check for collapsed or deteriorated rubber pads, particularly at the bellhousing mounts. One sneaky troubleshooting trick is to temporarily rig a piece of chain and a turnbuckle from the cylinder head to the driver's side frame rail and put just a little tension on it to prevent the engine from rocking as the clutch is engaged. If that cures or minimizes the problem, install new motor mounts.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!