are there size differences in ports between series six through eight...

 

I believe all the 13b-rew share the same engine plates/rotor housings through out its production (s6-s8) so yes they will have the same Port. I think the big difference comes between Models (13bt,13b-re,13brew) according the the parts diagrams.

 

the port on the side plates are the same size. just the runners are the difference