Have you tried using a RIMS mount? *ducks and runs*
No, really, it gave me a lot more sustain when I took the tom mounting hardware off my 12" shell. I tried putting it on a snare stand but that made it much more thuddy. I tried the RIMS mount with the tom mount still on the shell, and that didn't really remedy the situation. When I finally took that tom mount off, though...BIG difference!!! The drum sustains more, and it doesn't choke up so soon. It still chokes up a bit when played really loud, but I think that's just part of the package deal you get with vintage 3-ply Ludwig shells.