Again, this is FWIW;
I contacted the Pa. State Police, Department Headquarters, Bureau of Patrol, Division of Motor Carrier Enforcement. According to the Cpl. in charge the following is applicable to vehicles registered in Pa.
A Class B CDL entitles the holder to operate a single vehicle having a GVWR of 26001 or more, provided that any vehicle being towed does not have a GVWR exceeding 10,000. When I questioned him regarding the effect of GCVWR he advised it would be irrelevant. He advised that regardless of the towing vehicle registration, once you hook to any vehicle which has a GVWR exceeding 10,000 you need a Class A CDL.
Armed with this information, I went to the Pa. Dept. of Trans. web site, Driver Services Section, Pa. Vehicle Code-Title 75, Chapter 16-Driver Licensing, Section 1612, and there it was in print, as stated by the Cpl.