[JLMounce]

Final update on this.

After getting the engine back in the car for it's unrelated issue, I did decide to replace the motor mounts with a set of mighty mounts. Upon further inspection you could see the rubber starting to tear and delaminate from the steel casing.

Nothing changed with the vibration moving to new motor mounts.

After doing further testing to isolate the vibration, I did narrow it down to engine side with the torque converter dismounted from the flex plate. This week I replaced the unknown age, but seemingly in decent condition factory type balancer with a BHJ from Nitemare performance. I'm happy to say that the vibration is now gone with exception of a very slight buzz near the very top of the rpm band. Based on the drill marks present in the factory type balancer, I believe whoever did the rotating assembly on this engine back around 97-98 likely tried to neutral balance the stock balancer and there may be a slight imbalance in the rotating assembly itself. All of this likely masked by the poor and soft mounting the car had.

As I've replaced bushings, engine and trans mounts and gone to more rigid mounting of the subframe and suspension components, that slight imbalance is there. I've been beating on this thing for many years and I assume I'll be able to continue to do that. But, I'm socking away money for a rebuild at this time.