A833 Vibration Issue

I can tell you what it was in my similar situation. I had a bad vibration problem while driving and sitting at idle. It was bad at idle where the dash and the whole front end rattled. I checked everything and my problem ended up being a bad pressure plate. My set up was a 340 4 speed. So if you have access to a wheel balancer, spin your flywheel, then spin with pressure plate bolted up. You have to be able to mount it safely to the balancer. When I did this my flywheel spun zero. It was all over the place with the pressure plate bolted up. I was running a stock replacement pressure plate and if I remember correctly they weren't too expensive at the time. The pressure plat has weights on it too and needs to be properly balanced. In my case I think it was a bad reman possibly.