A-body was the designation for later '60s and early '70s Darts, just as C-body was the designation for larger cars of the same time frame. Sorry I can't tell you what the body designation was for your '61 Dart other than it was NOT a C-body.
61 Darts are big cars, some refer to them as C bodies, although Chrysler refers to post 65 cars as C-bodies. 62 Darts are B bodies and 63 up are A bodies.
Until 63 a dart was a bigger car I believe a B body the A body was a Lancer for 61 and 62 the Dodge version of the Valiant GEORGE!!
The Dart when introduced in 1960 was slightly smaller than Dodge's full sized line but also slightly larger than the compact Lancer line and it was originally based on the Plymouth standard sized model line with a few cosmetic changes. Although there was no official body designations until 1964, the 1961 Dart would best be classified as a "B" body. Smaller than the full sized models but larger than the compact line. In 1964 the name was given to the smaller Lancer line and the Dart became an "A" body. The original Dart line was given a new name Polara (which was the name originally given to the top trim level of the Dart in 1962) and it became basically a "B" body until 1965 when the name was changed again to Coronet. The Polara name was then transferred to the new Dodge "C" body design. So basically from 1960-1962 the Dart could best be classified as a "B" body size, and from 1963 on it would be an "A" body.
Well i am looking for a set of C body header, so if you want to get rid of them let me know. I may know where a tailgate is!
That's about as accurate an answer as you're gonna get. For '60-61, there were "big" or "senior" Dodges which rode on 122" wheelbase shared with Chrysler and DeSoto. The model names were Matador and Polara. Those same years, there were "mid size" Dodge Darts that rode on 118" wheelbases. The model names were Seneca, Pioneer, and Phoenix. They're not identified with a body designation like the later A, B, C, and E bodies. However they are unibody cars like the later B-bodies, so you might loosely classify them that way. I'm betting those C-body headers are going to have trouble fitting, as those (later) engine compartments are really wide which header manufacturers tend to take advantage of. Neat ride!
It was not considered a "C" body but it is true that it wouldn't be considered what most people think of as a "B" body either. That's why I referred to it as "B" body size which would be between the compact Lancer and full sized Chrysler of that vintage. However, it has the same wheel base (116") as 1962-70 Plymouths; 1962-66 Plymouth wagons; 1962-64 Polara; and 1963-4 Dodge 220/330/440. It is classified by AllPar.com as being "B" body size, (http://www.allpar.com/model/rwdbodies.html) even though that designation didn't come into use till later. It was not full sized as Dodge full sized cars of that era had wheel bases in the 117"-118" range.
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