Looking at it from another perspective, if the 590 cam was correct for the motor/car combo, then the XR286R really would really be “too small” to be optimum.

Looking at the OP’s sig says a best of 10.76, I assume that’s the old cam.
Then reports of 11.00 with bald slicks and running the much smaller and milder street roller cam...... which to me bodes well for the XR286R.

And, that’s not even taking into account that it appears “something” in the motor/car is going away.