Vin tag over rides what ever the cowl tag reads...the cowl tags were made by fisher body before the car was built so they made MOST but not all cowl tags that read either 118 or 116 as they didn't know what engine was to be in the car so they did the cowl tags that way.
Always go by the Vin as it will tell you what the car was born with. 115 Vin is correct with a six cylinder
Hope this helps,
This may help you some more...
http://www.novaresource.org/c67.htm
http://www.novaresource.org/cowltags.htm
Dave
67 Nova Boy