What main jet were you running with the big Simo? Your 13 stock jet was probably way higher than his 12 stock jet... What was only a few jet sizes for the 13 is a bunch on a 12. I ran a very similar setup to his bike.
Stock 12mm carb
Modded Airbox- I want to say that I drilled 5 or 6 1/4'' holes in it.
Proma Circuit Pipe- Very similarish to that Simo that you have.
I was running a 68 main jet and it was perfect... Topped out around 38 on flats, nice ride...