Welcome, I have heard where the vin tag and the cowl tags don't alway match. The vin tag is the one that matters. 6 clyinders did have the 135 vin, and the eight clyinder had the 136, and the SS models were 138 vins. I have heard where a V8 got put in a 135 vin in some of the earlier models but not sure of what year. Here's another site you could check out for more info.
http://chevellestuff.net/1967/vin.htm
Ray