Thanks for all the comments. I was 25 when I first put this engine in the car. I am now 62, and trying to remember exactly how it was is a bit fuzzy, but I still lean towards something with the 727, or possibly a bad balance job, though the latter seems odd since the components were balanced in 1979, and I don't remember a vibration when sitting still, and only after the 727 was installed. The last time the engine was disassembled was when I replaced the balancer with the Summit unit. I don't have any idea where that balancer went. My engine builder doesn't either. I wouldn't think the balancer is the culprit since I now have had three of them on the engine and the vibration began back in the 80's when the 727 was installed. The original converter I purchased for the 727 was a TCI. I replaced that with a Hughes neutral balanced converter when thinking it might be the converter, along with a Moroso heavy duty flexplate. As I mentioned before, nothing really changed. I keep leaning towards something behind the engine since the installation of the 727 (as I remember) seemed to be the start of the vibration issue. I am tempted to replace the transmission next as opposed to tearing the engine down to check the balancing job. I do think I will replace the engine and tranni mounts back to rubber. Though that is supposed to help with power transfer, I think it is only amplifying an issue that was there prior to this last build. The 410's don't help matters any, even with the GV. Maybe change to 355 or 323's. Like that off the line launch, but I want to cruise more than race. An ignition problem could be a possibility, though doubtful. I replaced the original electronic ignition with a DUI distributor and coil. Doubting the ignition because of the vibration being an issue of the past. Maybe a dowel pin misalignment. I have had the transmission in and out about three times in the past year, and every time things bolted up nicely. I will look into some of the other ideas some of you have had. Try driving in reverse and see if I can feel anything.
