Re:
If it were me, I'd change the entire chainset to a better one, maybe middleburn or xt/LX of the era to match the rest of the bike.
I'd change the front shifter as well. I may have a matching shifter for the LX rear one you already have if you are interested. I've also got an lx chainset that would go nicely (same shape/style as the xt m739).