Did GM not have an over head cam straight 6 in the late 60's? It seems to me that I had a friend at the time with one is his car. It seemed pretty hot for a faily small engine. What got me thinking about this is that I have a Jag sedan with a 3.8L (about 232 ci) DOHC straight 6. This car weighs a couple of tons, and flies with this engine.
I was wondering about the GM engine in a truck. I have never seen any references to it, and have searched this site without any luck.

Thanks
David