Most of the pt 142 sim schools have FAA approved prerequisites for their classes. Better check into those to see if you meet them. I heard for the pt 135 PIC upgrade class (Experienced Transition or whatever you want to call it) that in addition to the type you have to have some minimum experience (like 200 hrs right seat, not sure if these apply for King Airs). A guy told me that these are their most failed classes which is why the FAA required the pre-requisites. Just a heads up. Good Luck.