My '71 ain't a '71...or is it?

Hey all, just as the title says, I don't think my '71 Scamp is actually a '71. Here's the backstory:

I bought this 1971 Plymouth Scamp last summer with hopes to learn the world of Mopar, restore it some, and of course turn some heads. The gentleman I bought it from on Craigslist was very nice, had a VERY nice GTX in his garage, and the story he told was that he was basically downsizing and only had room for one classic car. The title had matching numbers to the car, all indicating that the car was indeed a '71.

Long story short, I wrecked the motor and in the process of rebuilding it, learned that the block was a '73. Okay fine. Someone probably swapped the slant 6 at one point for a 318LA. Which made sense because the car has the 904 trans (I think those were more for 6 cylinders and not V8?? I'm still learning here.)

Moving on, when replacing the heater core and foam seals on the heater box, the kit I got (68-72) didn't match AT ALL. The instructions said in '73 the heater boxes changed. Another clue.

So, here's my theory. I think someone had two cars. A '73 without a title, and a junk '71 (or at least a fender tag from a '71 that ended up on my car). Opinions???