According to the schematics, they differ on very few points - the voltage in the VH100R is quite a bit higher, and one capacitor in what looks like a low pass filter is actually smaller, which should result in a less smooth sound (the exact opposite of what you're saying). I may be wrong though, I'm not too good at spotting different functions in a schematic. The things that obviously differ are the transformers, which has an impact on the overall sound (esp. the output transformer). Your tubes and guitar make a difference too.. Your amp should also feel a bit tighter at high bass settings and also be a bit less muddy and cleaner at high-gain, but the differences are quite small.
Anyway, on to the mod -
Right after V2a you see C9, which is 22 nanofarads. For fun, try swapping it out with a 470 picofarad one, i don't really see how it will help, but it will make his drive channel exactly the same as yours (this exact circuit puzzles me, it seems like a lowpass filter and a voltage divider, but I'm probably wrong).
Now, if that doesn't work, move on to right past V3a, where the tone stack is. Replace C17 with a 680p silver mica, and test the amp. If you still feel it's too harsh sounding, try replacing C22 with a 33nF Orange Drop, this will make the amp a tad bit warmer and darker. If it's still not enough try a 47nF, it will give lots of low mids and not so much high mids, very warm sound.
Doesn't have to be these brands, but they have a good name.. not that it should matter. You could just as well try radio shack, make sure you get mica and polypropylene caps (mica for the really small ones, polypropylene for the others). Don't get polyester film, they're for vintage freaks who like noise and distorting capacitors (which is not good for high gain).