Marty
I have trued both the stock, treaded rear tires and the standard slick rear tires with no issue. I was surprised to hear that you had trouble with the stock fronts. In my cars, the stock fronts were already pretty round and I have not noticed any issue or bouncing of the front end. I have not yet tried truing the stock fronts.
The Thunderslot McLarens would be welcome in the series, pending a check of the cars for differences. If there is a difference in width, we would need to have a track spec. I was hoping to get by without one, just using the rule about extending past the body. I have noticed that the roadster Lola body may be slightly narrower in the rear than the coupe. In my swapping of chassis between the coupe and the roadster, I did not adjust the chassis when I went back and forth. The roadster was just slightly faster, a factor that may be mitigated if it can has a slightly narrower rear track.