Still dealing with this issue. Runs well until it gets up to operating temp. Turns out that my cap and rotor both burned up. Swapped them out. still jumping tach. Swapped out the coil. Still jumping tach.
Replaced the distributor, cap and rotor again. Still not fixed. I've suspected the MSD from the very beginning. Swapped in my original Duel Point. Haven't gotten the car started yet so I don't know if removing the MSD from the equation is the fix or not. I'm going to tinker with this for now, but I did pick up another MSD to swap in.
KID