It's from the seventies or earlier and may have been in an Ace Double. Earth has been invited to send an ambassador, or possibly an individual who will be evaluated as proxy for all Homo sapiens, to an interstellar multispecies organization. Unable to settle on an individual representative they graft multiple complete minds of at least 7 people together in one body. The aliens are aware of what has been done but just believe it makes failure more likely and allow it. The grafts do fail but the result is a new, stronger mind rather than a broken one. The writing style is, in my memory at least, similar to C. Sheffield's, but I don't remember enough detail to be sure of that.