They must be the original cars from the Trans Am/A-Sedan era with(I believe) 3 actual Trans Am races under their belt or a vehicle with significant non-TA History(such as the Yunick 69 Boss) but remember, many original A-Sedan cars back in the day also never did any TA races hence they also don't comply.
My Boss302 is outside this criteria although back in 2010 they did allowed me to start from the rear at SAAC 35 Somona which was really an unofficial Historic Trans Am race...…..it was a bunch of FUN and they made me feel quite welcome. Dale M