I have 3 of them. All are used. (64 riviera, 67 coronet, 79 camaro) The oldest one had an analog brain box (64 riviera) and I had no issues with that. The other two have the digital brain box and I can have a problem if I turn on something with a high electrical load.

I was talking to some companies that have have gps speedometer senders that have relays built in to automatically turn on and off at certain speeds. So far the prices were a bit high for me to pull the trigger on anything.

As for vibration. (79 camaro) only one of my cars has a problem. Vibration gets bad at 65 and goes away after 75. I've had the shaft balanced twice at a driveshaft shop and each time it got better, plus I checked the angles and all is good. Thinking I need the shaft balanced at a driveshaft shop that does high speed balancing. Most driveshaft shops don't have the capability to balance over 900rpm.