I had a 54 Mark VI alto a number of years back (57 XXX). There is something to the necks of this period. I understand it is very similar to an SBA style neck. These horns have a tremendous tone. My horn was set-up by John Weir with domed plastic resonators on high quality Italian leather pads at the time when I purchased it. It was by far the best Selmer alto I have ever played. I have always wondered what it would have been like with the original resonators.
SBA alto can be setup with a light, precise and blazing fast action if rebuilt correctly. In my experience their main downside is a limited choice of mouthpiece design in order to achieve neutral intonation tendencies. That being said with an Airflow contemporary of the horn they are In my opinion very good classical players. A pulled down neck is of concern should it affect intonation or harmonic response, after market options do exist, however one has to start questioning the cost/benefit at some point...