5 on calculus BC allows skipping Math 1B as well, but you may want to try the old final exams before deciding whether to skip Math 1B (or 1A). You may have to self-study the introductory differential equations material in Math 1B before taking Math 54 if you skip Math 1B.
Old final exams: https://tbp.berkeley.edu/courses/math/
Have a list of alternative courses to sign up for in case your first choice ones are full.