Correct. I did most of it in a complex but ran out of time. We got the commercial stuff done day 1 but left the PTS stuff for the following morning. By then the 172RG was busy but Skyhawk was available. I do not think you can use a Champ for everything, but there's no harm in asking. Just be ready for a "no" since it is not in agreement with the FARs to use only a fixed gear airplane for the exam.