I have planned to do all you have suggested this week including adding the soft mount. I am pretty sure the throttle shafts are not synced based on a compression test I did with the throttle closed. The rear carb is expected to be nearly closed given I can only achieve about 60-70% of the front 2 cylinders. At open throttle that are all nearly the same.
By the way, thank you for the information. I appreciate your taking the time; it is a big help to me.