Just to clarify, the original shift knob for a GT500 is the plastic, blue racing striped knob, with the shift pattern.
In contrast, the GT500 KR was supposed to use the wooden “Cobra” shift knob (without a shift pattern) . The brass shift plate was designed to compliment that specific application.
Even though the wooden shift knob was not used, KRs did end up using the brass plate.
I dont believe the brass plate was used on the GT500. It was actually designed two months after production started and by that time a good number of cars were already completed.