Well, there's lots of clues to let you know about the configuration of a car: hood types, hood/fender decals, the HP plate insided the cockpit, aircleaner decals, other stickers in the engines (IIRC), carb setup...
If you know what was available in a given year, all these can help ID the engine type. For model info, you can go to the CAC model center or to sites like the technical resource page at
Idaho Vette .
Of course, if the car has been modified from original, then the above might not help much -- although it could still yield clues as to what is in the engine bay and what should be in the engine bay.
The only surefire way to tell, I believe, would be to pull some numbers, such as the VIN, block numbers, manifold numbers, etc. To get more info on pulling numbers, do a search in this forum. This'll tell you what should be in the car, what is in the car, and when some of the components were manufactured.
Now, I'll give you some examples: I once went to look at an 1969 L71. When I got there the first thing I noticed was the L88 hood. When the hood was popped open, I saw that the L88 hood was not original and that the 3X2 carbs I expected had been replaced with a single 4bbl Holley. I believe the HP plate corraborated the L71 claim, but I can't quite recall. At any rate, alarm bells started sounding and if I had been interested in pursuing this car I would have pulled the engine numbers and the VIN (but the guy upped the price by 50% when I got there, simply by saying "US dollars, please" so I just walked away).
When I went to see my LT-1, well it was obvious from the hood and the HP plate that the car was supposed to be an LT-1. Looking in the engine bay I saw a 350 with a big 4bbl Holley, the correct intake and exhause manifolds, and an emissions sticker that all corroborated the claim. I checked out the VIN and found out that the car was supposed to be an LT-1, so things looked good to me.
Anyway, long story short, familiarize yourself with the different model configurations and get the numbers. I always took printouts of the model info so that I could compare. If in doubt, take pics so the people here can help, and/or take the car to a vette mechanic shop for their opinion.
