I've been adding ACI labels to everything in service prior to 1977 for my 1980 era.
Looks like in 1980 you are off the hook on locos, as all the Conrail locos tagged in 1980 that I've seen are sans ACI.
Here's one stenciled CR in 1977 still with it from an earlier scheme:
http://pc.smellycat.com/pics/equip/cr2289b.jpg
Roger that. My only ACI-labeled loco is a PC paint-out SD35, per proto-photo.
I'm leaning toward getting 2-3 of the ESM gons, 1 each in CR and PC for sure... and maybe circle keystone Pennsy for 1956 (the shadow keystone paint date listed on ESM's site is 7/56, the very month I model for my PRR roster, and would mean I couldn't weather it!). The PC gon will get an ACI label.