I asked about tubes because I think NOS preamp tubes will make a difference in tone. I replaced tiny trannies on a DC-3 with Hammond trannies and was quite pleased, but I don't think replacing those big trannies on the Mark V with Hammonds, Mercuries, or whatevers is gonna do anything for making the tone better.
I haven't owned a Mark V but have owned a Roadster and a Lonestar, and I can say that NOS preamp tubes sound better than stock Mesa preamp tubes.