[Jack_Bauer]

I'm assuming you're meaning the 60s Elan here, not the 90s FWD Elan (which is sometimes referred to as an S2 also), right?

It doesn't seem that implausible to be honest. Autocross is mainly about a) the car's agility and nimbleness (is that a real word?) and b) driving talent. The old Elan weighed probably less than half of most of the modern day sportscars competing, so it doesn't really need big fat wheels and tyres to get good grip. They'd only increase the unsprung mass and mess with the steering response and wheel control. Plus 120bhp isn't really too shabby for a car that weighs next to nothing, and power isn't the most important factor in autocrossing.

I don't have corroborating, but I don't think it's too far fetched to imagine a very well driven Elan keeping up with the likes of Ferraris, Porshces and Vettes through the twisties.