Yeah, I know...... But I had been chasing a rumble for a while at that time and decided to go with same-sized rims to help isolate the source. It didn't work, but years later I discovered road force wheel balancing, instead. 
The 7" rears with 225's on them, along with 3/4" anti-sway bars front and rear and Koni shocks (or maybe Bilsteins back then - can't remember), would not let go, no matter how hard I tried on a couple of tracks. You could feel the limit of the sidewall flex and after that it just held on with no indication of oversteer up to the limits of my courage. Other, more powerful cars were left behind (until the next straight stretch) while it just carved through the turns. I was running Continental 50-series back then - decent tires, but it took LOTS of weights to balance them.