I've never tried a Morgan vintage. So I can't say it's not a good thing. For the best intonation, large chamber mps seem to work best with Buffet saxes from my experience. Others here have said the same. The smaller sizes I've tried made the notes above A2 go sharp without me making adjustments.
I use a Morgan 6L for jazzy stuff on alto. I sold my Buffet tenors (DA & SDA)but would go with similar mps for those. That said, I use a S80 C* on my SDA alto for concert band and that does the job just fine. So, YMMV