Those were the Guilford years..I visited that yard several times during that era..
I never once saw an actual switcher..(an SW-something)..
switching was probably done by "road power"..D&H and Guilford GP38-2's and the like..
They might have kept a few of the D&H alcos as local switchers during that era, the last of the RS11's..
I dont think they went out on the road much during their last years..
but I never noticed which power was "through power" and which might have been dedicated yard power..
As far as I know, anything that Guilford/D&H/Susquehanna had on the roster at that time
could have been switchers..but no actual "switchers"!
If there was dedicated yard power, it probably would have been the smaller and older road switchers..
the last of the D&H RS11's..(No RS3's or RS1's by the mid-80's) (C420's and C424's were road power until the end)
B&M had a few GP9's that were floating around on Guilford during those years..those would be contenders too..
Or they might have simply used whatever power was handy at the moment..there was always a lot of power around..