I ruled out an issue with the PS pump by running the engine with the PS pump belt removed. I verified tightness of motor mount bolts, trans to engine, steering box to K frame, and flex plate to TC. I did not remove the motor mounts, the rubber looks good, no sign of any cracks. Cranked over engine while watching flex plate and TC, did not see anything unusual. Reinspected what I could see of flexplate looking for cracks or looseness at crankshaft. Used a small prybar to see if I could move the TC in any direction other than in the normal rotation and everything was tight. Pulled the dizzy cap, all good there. Ran the engine with car on lift and looked at TC. Did not see any obvious imbalance or vibration. I could feel some vibration when I laid my hand on the trans bell and on the trans pan. The engine seemed much smoother, although there might be a very slight vibration. So thinking I'm at the point where things have to come apart. I'll likely pull the trans from the engine to more thoroughly inspect the flexplate and most likely replace the TC as many of you have suggested.

I've not checked into a vacuum leak being the source of the vibration. As I said starts easy, runs cool, has good power, and no ping that I can detect/hear. I cannot feel or detect a miss in the engine. The RPM drop test seems to indicate that each cylinder is firing. The vacuum gauge is steady at 15" at idle. I would have expected a bit more, maybe 17 or so. Will spend some more time on this while I'm trying to lineup a replacement converter.

Thanks for your thoughts and suggestions.

R/ John