Canadian National order six A-B sets of the CPA16-5 cab units and the CPB16-5 booster ("B") units in 1954.  These B units were five-axle B-A1A units, the first for Canada and the first for North America.  The units were delivered from Dec. 1954 through February 1955, in the classic green, black and yellow trim and yellow nose.  The B units were numbered from 6800-6805.  They operated on name trains between Montreal and Toronto, Montreal and Quebec City, and Montreal and Halifax.  All of the units were repainted into the new CN "new image" scheme after 1961.  The C-Liner A and B units lasted until their retirements in the 1967-1969 period.
The trains always operated as an AB powered consist, so if you have reserved/purchased the A units, then you need to have the "B" units to be prototypical.

PLEASE NOTE - The same picture below is a freight body shell on the 5 axle chassis.  It was quickly and partially modified, just to give you an idea of what the B would look like on the 5 axle chassis.  It is not prototypical, we know that.  So before you start critiquing the model and the project, wait.  The B shell is going to have changes made to the tooling to make it prototypical to the actual CNR  "B" unit.   Once we have a modified B unit shell, we will be posting pictures of it.  <Picture 1>   <Picture 2>   We show you some artists rendering of the applicable B unit.