i changed to a fender choke and it seemed to help the sound. i havent tried different PT and OT though.
Also just an FYI i wouldnt bother spending the $300 or however much the MM power tranny is just because the actual PT doesnt have any effect on the sound. (mercury magnetics will try to convince you otherwise for obvious reasons. $$$) the voltages do matter though. And different voltages doesnt garentee better tone. It could easily ruin the tone. A different OT will definatly change the sound though weather it's better or worse is totally up to your ears.
It's too bad there aren't really any sound clips comparing transformers on a overtone, being it's an major expense and not the kind of thing that easily swaps in and out.
However, I think I'm pretty satisfied with the amp's sound. I only just finalized my mod today. I wanted to be able to get a mellow horn like OD, and pretty much ended up with an OTS but with a few differences.
In sequential order around the circuit they are:
1) V1a plate/cathode changed to 120k/1.8k;
2) V1 cathode caps changed to 10uf;
3) Bass control 10k resistor to ground removed;
4) V1b to master volume coupling cap reduced to .02 (from .05);
5) Master volume 47pf bypass cap removed;
6) Switch added to 47pf cap across 470K resistor at OD stage entrance;
7) Three way switch adding .0062 cap; .0022 cap; or no cap; to ground before 470K resistor at OD stage entrance; (treble bleed);
V2a to V2b coupling cap increased to .01 (from .002);
9) V2 cathode caps changed to 15uf
10) External PI trimmer pot;
11) Short black plate RCA at V1; JJ at V2 and PI.