Rear Swaybar options w/ RMS StreetLynx

I've been experiencing major understeer and some body roll in the autoX and my front tires (Nitto NT555, I know not the best autox tire) were rolling over, even inflated to 40psi. I thought I'd start with stiffer springs, better tires, a fatter front sway bar, then a rear sway bar. I've 4 corner weight balanced the car and went to 550lbs front springs and 400 rear which helped a little but not much.
I've talked to Bill several times about the issue and he said he doesn't make a rear bar, nor should I need one. He's a great guy and graciously had his supplier bend up a 1.25" front sway bar for the Early A bodies, which he didn't have before (only 1.125"), but is now going to ship his alterktions with the bigger one; you're welcome ;-).
I'm working to get my car ready for next season and researching going from 17" wheels (245s on 8" and 315s on 10.5") to 18" (235 on 8.5" and 275s on 10.5") w/ Bridgestone RE-71Rs, and also researching rear sway bar options, hence the question. Who knows, I might find I don't need one and saving that solution for last.
I have FirmFeel front and rear bars on my 66 valiant and it feels very balanced on the track, even leaning toward over steer which is ideal in my opinion. Granted this car is square, with 215/45/17 tires all around.