I own an Excelsior Symphony Grand that was owned by Charles Magnante, the only difference from the "standard" Symphony Grand is the treble keyboard where he had custom sized black keys installed which obviously also meant the white keys had to be cut differently to accomodate them, that were slightly thinner than on the production model.
It plays as well as the number of other Excelsior models I have including another Symphony Grand, with 140 bass m lll extra bass row tuned concert, 911, and 940. The 940 is my "work horse" tuned concert on the bassoon reeds and musette on one of the middle reeds,, concert on the other and the piccolo concert, but I will use the other instruments for various genres, the 911 is LMMM tuned Musette, and another Symphony Grand tuned concert. Lately I have been using a Roland FR-8x digital accordion for a lot of performances, but I love my Excelsiors., but the sound of the jazz reeds that were employed by Roland was from the Excelsior accordion. One of my Rolands (I keep one on the East Coast and one on the West Coast) had a manufacturing defect where the bellows had an air leak where it met the bass side of the accordion in less than one year and have had the accordion almost a month and I am still waiting for it's return repaired, I have Excelsiors that go back to the 50's and none of them has lost compression or developed leaks like the Roland did. Roland should perhaps had learned that the pins that hold our bellows on the Excelsiors would make repair easier than their method of attaching bellows by glued gaskets and pressure closure as was described to me by a Roland Repair Manual and Repairman. I have never had a problem with my Excelsiors and repair people have always been able to deal with any minor problems that have occurred over the years. I miss the late Tom Bruno who worked on a number of my Excelsior accordions.