IP had a corrugated box plant on Aroostook Valley RR in Skyway Industrial Park (the former air base) at Presque Isle... Opened early 60s and closed in the early 90s (?). It's still standing. If you Googlemap it, it's the first industry you'll find as you follow the industrial track leading into the park (IP shared the spur with a potato meal processor and another industry - memory escapes as to what they produced, but the building appears to have been largely dismantled). The street view is the giveaway - the building is IP blue. Possibly the plant outlived the AVR and was served by BAR while under Iron Roads control?
So there is an exception to the rule that IP in Maine was always on MEC. Also explains how AVRR hung on for so long. I could never make sense of that.
I am familiar with the business park and building you mentioned. Thank you!