The earlier converter (yours) has a smaller diameter snout than later engines..... I think 66 or 67 and after. You can “bolt together just fine” the smaller size into the later crank with the bigger hole, then the flex plate bolts are the only thing centering the converter to the crank and in a short time you will have problems. You can check this by unbolting the flex plate from the converter- if you can wiggle the converter around off of center when it is up against the crank then you have a problem there. I’m just throwing out ideas here. I really didn’t see any bad vibration problems in your videos.