Keep an eye on the oil pressure for a while. A buddy of mine wound up losing his 2.7L motor that way.
After overheating like that, the oil pressure started a one-way journey downward...
I don't know what could have caused yours, though. Your SC should have the "trombone" cooler, so checking the t-stat would be a good idea. But even without an external cooler, I don't think 4 laps in mild weather should have been able to overheat that much!
Could there be an oil pick-up problem? There's something about the early SCs and the oil pickup... I think if one of the sump plates is put on the wrong way around (which isn't hard to do) the pickup doesn't work very well?
--DD