In Australia we had Valiant chargers with 340 autos in them and when imported they were going to be a race car but our gov came down on performance cars ( thought any pimply faced apprentice could buy a 150 mph supercar?) so the 340 chargers were only offered with auto, single exhaust and 2.92 diff. A mate had one and his only modification was twin 2 inch exhaust system and he used to take it to the local drag strip and just left it in drive and it ran 14.2 sec qtrs with the stock ER/70/14 tyres! With a lower diff ratio and better tyres it would of been in the mid thirteens pretty easy!
At the time our performance XY Falcon GTHO Phase three that won bathurst ran 14.8 sec qtr according to our motor testers but would pull 145 mph down bathursts conrod straight.