As far as the vibration did you ever have the driveshaft off? If so you may have put it on wrong and it's off balance which is creating the vibration. Take it off the pinion yoke, twist it over about 90 degrees, and reinstall the bolts. The shaft is balanced from the factory a certain way and if you don't mark the way it was on there from the factory and you reinstall it differently then it'll be out of balance. Hope this helps.
As far as the motor, how's your spark plugs and wires? Checked your plug gap lately? Maybe the plugs and/or wires are bad. It's a place to start anyways.
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1967 Mustang Coupe
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