If it never had the vibration before I would check a few things. Are or were any of the 4 engine mounting bolts run loose, and if so are the mounting pads worn down causing the misalignment? If so shim it up. Unhook the chain coupler and feel the transmission input shaft for play. If the tapered roller bearings are loose this will also cause a bad vibration.
I like the idea of the alignment bolt to tweak it perfectly, however I"m wondering if there is not a cause for the misalignment.