I've not had many problems with older saxes being temperamental with mouthpieces, although my Conn 6m definitely prefers my Lawton BB and doesn't get on with older style large chamber, concave baffle mouthpieces at all.
I've tried all manner of mouthpieces on my Martin Indiana and Medallist altos and they all worked fine - Lawton, Berg Larsen, NY Woodwind, Otto Link Tone Edge, Zagar, Jody Jazz HR*, Runyon - 22, XL, Custom
The Jody Jazz HR* is the nicest for ballads and the Lawton is good for slaughter and mayhem..
Martins have a reputation for having slightly wayward intonation and I doubt any mouthpiece will be the magic cure for this - saxes like this were designed in the days when it was assumed the player was responsible for the intonation, not the instrument - but does any saxophone play perfectly in tune?
Indianas are never going to be as desirable as other more fancy Martins, but they're fine instruments if you like that plummy sound and the quirks of older horns and you'll never find a LH thumb rest as comfy as the "heart shaped" one on an Indiana..
people moan about the ergonomics of vintage horns, but they suit my small fingers better than the modern ones and at least I can reach bottom Bb without a major expedition
for more info on Martin saxes -
http://www.themartinstory.net/version7/index.php
and Mr Howard's comments are always worth a read -
http://www.shwoodwind.co.uk/Reviews/Saxes/Alto/Martin_Handcraft_alto.htm
enjoy your instrument