Quick Fender Tag Decode Help Please For 1971 Dart

Special order engine? 400 cu in 2 bbl? WEIRD!
Got this from a decoder that has both VIN and Fender tag decoding. Not sure where I saved it from
Sounds like an odd car, if so. Do you have it? Any evidence of a big block?

Also, on the build sheet template that I have, it says spec. engine in the F 0- slot.