A mystery indeed.
According to this thread, somewhere in the the 600's is supposed to be where they switched over.
http://www.zr1netregistry.com/forum/...ead.php?t=1293
Perhaps because it was an export car they held up production on it until after the 600's? Maybe there was some kind of delay getting the ZR1's certified for international deliveries and those cars were held back until after the switch over.
I'm just guessing.
Regardless, Welcome to the Brotherhood of The Beast.
TomC
"Crabs"