If you tell us what the VIN is, we'll tell you everything you want to know about the car. Well, not exactly true, but we can tell you when it was built, and whether it is definitely a pre-L, definitely an L, or made sometime during the transition and it is difficult to say.
One thing that is easy to say is that if it is a 1971, then there is no way it is an L. They hadn't been "invented" yet. This is neither good nor bad, as an "L" has no more or less value than a "pre-L" - it mostly comes down to which do you prefer more.
You ask how you can tell if it is stock? If it is a 1971 car it will have small chrome bumpers, front and back. Later model cars had large, black rubber bumpers with hydraulic ram-things... If it is a '71 with these bumpers then you know someone has modified it...
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Charlie McCall
1985 DeTomaso Pantera GT5-S #9375
"Raising Pantera Awareness across Europe"
http://briefcase.yahoo.com/gt5s_1985
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