I haven;t had much experience around the C12 or the 251, but I've been abound a few U47s, although it's been a while. Arm yourself with a large bag of salt to be taken frequently.
I can address the bottom of the heap mics. The Marshall V67G has a similar magic to my ear as the U47, although I would really need to hear them side by side. Same with the Oktava MC012 and the 33mm LOMO head - a magical combination.
I've heard the Brauner and the Soundfield and both are wonderful mics, but too detailed to fit the U47 sound. The T.H.E. mic with the 33mm capsule also sounds very good to me.