I'm hoping someone can identify this for me. I'm in super early stage of trying to restore a 74 360 that's just basically a roller with many parts missing. This weekend I bought a 76 dt250 and a 1975 that the guy claims is a dt250. The label on neck says it's a 75, however it looks to have a dent free and only surface rust inside fuel tank. It's a bare dirt bike with no lights at all. There is a factory lock on left side of neck basically. The stamped number on neck is 501-202812, I haven't found a number on engine yet and haven't had much chance to look very closely as I've worked all weekend. Thank you for any help. 

VIN tables and lots of useful info is in the tech library here.

frame number should be a 75 DT400b

Thank you MarkT, I've actually been scouring all the vin tables but because it has 250 engine and what looks to be a 74 fuel tank i never even thought to look at 400 vin numbers. I'll look there now. Again thank you. Actually after looking at dt 400 vin using the entire vin though bike is labeled on neck as a 1975 per the vin table it's shown as a 1976 dt400c. I would have never have guessed that 

So do dt400 cylinder fit on a dt 250 bottom end or are they all different with their individual bottom ends. I was surprised to discover a 250 engine in a 400 frame 

Engines swap, top ends don't.