Since cars had to be 3 years old, ITS RX-7s didn't race until '89 at the earliest...
The dual purpose aspect remained in place for quite awhile. I remember driving my car(And RX-7) in '93 from CT to New Hampshire and having to0 stop every 5 gallons, cuz the extra weight rubbed the tires too much, (where the "I thought those were crap when I welded them in" Ground Control panhard rod brackets ripped out making the car go all "railroad car" crabby,) and to Lime rock (where I won MONEY!!!!), and to Pocono, where I totalled it in my school, (but still got my lic) and to the Glen where I done blowed up the motor, (and rented a car to get home, then "borrowed" my bosses van the next weekend, and found out why you need trailer brakes on a crappy van when I ran thru the stop at the bottom of the hill leaving the Glen and drove over the funeral homes sidewalk..and I swear I never went over 30 the whole hill.)
Yup....dual purpose race cars. good idea!