Actually, the older Stilettos cannot be made to sound like the new versions. It seems that the newer Stilettos have not only more gain, but have also been revoiced.
The old ones can be modified by Mesa with what's been called the "Hollywood Mod". Seems it adds more gain and bass response.
Regardless, the amp was an incredible deal at GC, and sounds very good without any mods. I know for a fact that Mesa was not happy about GC blowing them out at half price.