My car might be a fake? Please help.

Hey everyone,

First off let me say this site has been a wonderful source of knowledge and information.
And you all have already help me quite a bit.

Now for the story.......

I recently bought a matching numbers 1970 340 four speed Dart Swinger. (Or did I)?
let me explain....

When I bought the car I got the original Build/Broadcast sheet.
The fender tag, dash vin and build sheet all match.
So I didnt think to much about it.

So today Im doing some interior work and pulled the back seat and there was another build sheet. It is a build sheet for a slant six. My car has the 83/4 rear end and the 4 on the floor 340 motor.

How can I check to see which sheet is correct? Are there numbers stamped somewhere else I can look at.

Also the fender tag is screwed on. Shouldn't be riveted?

I have two theories....One is that someone put the fender tag on, switched dashs, swapped the motor, trans and rear end. and put all that in a donor slant 6 car. But That seems like a lot of work to try to fake a true 340 car.

My other thought is that someone simply put in a back seat from another car and never saw the sheet. Please let me know what you guys think.

Im not sure what to do.

Thanks again everyone.