Many of the guys are just "excersizing" their cars. They are not former racers and have a large investment under them and are also of "senior" years.
As an example, at the 2013 Glen SVRA wkd. with the HTA cars, the fastest qualifier did a 2:10'9. At the 72 Glen T/A race the fastest qualifier
was Warren Tope with a 2:03.7. The only "factory" driver was George Follmer who was 2nd.
Bear in mind that the guys running HTA cars to-day have the advantage of more HP, better brakes, etc. Add maybe 3 secs. for the bus loop turn
they are still almost 5 secs. slower. Warren was good but I'm guessing that Parnelli and Mark were probably 1-2 secs. a lap quicker back in the day.
The longer Glen track with the Boot was only used that one time in 72. Note that turn 1 seems "improved" and is faster now.
Robert Barg