we have mainly 6 axle units on the B&A Most of the Mac's seem to have ,migrated south. Also, cab signal systems is another factor. If you see a 4 axle as a leader it is usually when there is a power-shortage. Sometimes if a 4 axle needs to be moved east from Selkirk it wll be used as an add-on to atrain that has come into Selkirk destined for Boston that has no cab signals.
Conrail used C30-8's and SD40-2's.....and of course the wide-bodies once they arrived on the property.
here's a site you muight want to follow for current happenings on the B&A. http://finance.groups.yahoo.com/group/CSXTSightings/