Thought I'd add an end-of-season update as to where we're at with the car.
A mid season converter change helped. We picked away at some other small things and also found some improvement. As it sits now, the car is a solid .80-.85 under in decent conditions (no altitude correction) in this part of the country. A good barometer here is 28.8 (uncorrected) so I'm pretty pleased, all in all.
Where I go from here with it, I'm not sure..but it's been fun!