I have two tenors a Conn 10M and a Grassi Pro 2000. Both are cool saxes. I decided to try out the Grassi crook on the Conn for a laugh, and because it looks more modern. To pad out the slight different in neck size I ended up getting a square of kitchen foil, doubling it a few times and then wrapping around the crook to make a 'solid seal'. This really worked well! Creates an instant hybrid. Next I put the old 10M crook back on, with a thinner foil to try and get a better seal which was a little loose. And this really improved the original sound too. Making the seal more solid seems to reduce damping on resonances in the metal, which then get worked into the air column sound. So now I am thinking the mouthpiece cork could be replaced by shims of this type, although I haven't tried it yet. Anyway, folded foil is now an essential item in my bag.