The image labeled a 12-D at the BOCN is indeed a 12-C. The clipping on the main fins is also shown on the example from the USAF Armaments Museum at Eglin. Both were labeled as 12-C Bullpup B

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Gravity is a harsh mistress
SAM 002
NAR 91005
"The complexity of living is eminently favored to the simplicity of not."