Look for a ":91" stamping cast into the backplate. As far as I know, all target drone engines have this designation with no other markings other than the K&B logo and "Made in USA" cast into the side. The Carburetors are often machined differently and my two drone engines had no pinch at all. All of my other sportster engines (the other three models) have a tight pinch at TDC. The lack of pinch may be specific to the drone engines since they weren't broken in prior, just fueled, fired, and launched. I've heard of "regular" .65s having a good pinch like my 28 and 45 have.