The picture you refer to on this site and that was published in the Hamburger Abendblatt newspaper, is, according to your description, this one :
Attachment 17403
and the guy next the Supremes is definitely Chris Howland :
Attachment 17404
Attachment 17405
The information in this newspaper and the photo add a lot to the fact that Musik Aus Studio B was taped before April 1965.It also adds a lot to the fact that March 29 become the most probable date for its taping.
I also become more and more conviced that the supposed tour in Germany around March 15-17 is not the correct information. I have to check again what's exactly written in billboard, but I think they considered the fact that the Supremes were in Germany for a concert for the press and a tv show as a tour in Germany, when for me a tour is concerts in several cities of a country...