modify to the specs that you mentioned above? it depends on how you want to go about it.
1. get something like that SG copy aboce and have a luthier add an additional two frets. it can still fit.
2. but what i would do is get a set-neck PRS 24, Ibanez (or any other superstrat) and install dual concentric potentiometers para walang invasive or non-reversible modifications na gagawin.