Thanks to John Tarabocchia for providing me vintage ads and informing me of this model.

This horn is the immediate forerunner of the famous Super Dynaction. It's also not that much different from the "SA" horns: the obvious difference is just the change from the "resonator" bell-to-body brace to a flat, sheet-metal piece (this is also the easiest way to distinguish these horns from the "SA" model).

I owned a Dynaction alto and it was the all-around best horn I ever owned.  The intonation was great, the action superb: slightly more cumbersome, but a lighter feel than the Mark VI. The sound was dark and lush. 

I have had two other professionals, whose main horns were Mark VI's and had never played a Buffet, play my horn. Both said that my horn was "comparable" to their horns that cost thousands more. When I finally got my hands on several Mark VI's, I decided that they were right. This is kinda kewl because this model Buffet is supposed to compete with the Selmer Super Balanced Action horns -- the VI was introduced in 1954.

I had the opportunity a few years back to compare my horn (which was mostly mint: some relacquer and repair on the neck) with another Dynaction in a lot worse shape and I can conclude that the original setup of these horns included THICK flat metal, screw-in resonators. That not only gives these horns the traditional dark Buffet sound, but also provides a bit of projection.

As mentioned previously, it seems Buffet "restarted" their serial number charts with these horns and these seem to be the first horns that follow the "standard" Buffet serial number chart.