Okay, here is the info. I have been able to come up with so far. These numbers are not precise however I think they are close.
The production number is somewhere around 407,142 +/-...
86% of Chevy trucks in 1960 were six cylinder. 14% were eight cylinder or about 50,000 trucks. I don't have the breakdown of stepside versis fleetside.
I wish the numbers were more precise. I do believe Chevy made less 450,000 in 1960. And I'm sure it was around 410,000.
Something interesting, by 1966 Chevy produced 250,000 V8 pickup's, which is a 60/40 split for sixes versis eight's.
Hope this helps...