Slant 6 Vibration

BTW, and exhaust leak by itself usually does not cause engine vibration like you show; an intake leak or valve misdajustment are better candidates for that, among other things.

Since you have compression test on your list, I would do that first as a baseline of what you are working with inside; no sense in doing everything else and then finding you have a burnt valve and having to tear the manifolds off again.

Run the compression test with the throttle propped open, pull all plugs first, and run each cylinder 4-5 times around and take readings. Post here.