In ChoatieKid’s experience, the regular BS curriculum more than prepared him the AP exams he took. For APUSH, his history teacher held two evening sessions to go over peculiarities of that particular exam. For the other two, no additional prep sessions needed. The “self-study” was the same study necessary for passing any term exam in those courses.
I think the concern with the block schedule is the length of time between the end of an earlier course and the later/end-of-school AP exam date which might require refresher self-study.