It would have to have a 60mm stud spacing with a 28mm port opening just for starters...The P-85 stock exhaust is more that adequate and the motor produces more power than you could or would ever use on a bicycle anyways, so why even bother???...It's a great motor just as it is, It does not need modifications.
Most folks are never gonna be convinced of this unless or until they get to actually try a Phantom out and then they will finally know why you and I are both of the same mind that they do NOT need any modifications for more torque power or to make them go faster.Throw an mz65 on any other 2nstroke, yd100, 80cc, firestorm 80, etc and they get a little power boost but work without issue. The Phantom makes a metric ton more torque and probably double the horsepower of those engines out of the box.
Even if you went to town on any standard motor it would barely touch a Phantoms out of the box power, or at best, match it.
They will never be able to use all the power they have in a P-85 right out of the box as it is.