The Pa regulations on the site are very bad. They really don't tell you anything other than what you don't really want to know! The whole site runs you round in circle's but never give you the information you were really looking for. Beleive me I have tried!
You may find this helpful.
PennDOT Driver and Vehicle Services - Classes of Licenses
Based on those 2 links you do not need a class A (combination) license.
We may have misunderstood you though, are you asking about a combination registration?