MILW (and GN, NP) helper stations?

[wjstix]

Well NP used helpers to get empty ore trains out of Duluth/Superior !! The tracks at Allouez WI are pretty close to water level, pretty steep climb to get out of the 'bowl' around the Twin Ports and get trains on level ground going towards the Cuyuna Range.

One factor about a rear pusher's location was what how the caboose was constructed. A car with a steel underframe could withstand the pushing of an engine behind it (even a woodsided caboose) so the engine could couple up right behind; an all-wood car would have to be cut in behind the pusher engine.

[JanOlov]

With all this mountains with heavy grades and trains, where did Milwaukee Road (and GN, NP) have its helper stations? How was this helper traffic operated with the cut in and cut off? What decided where to put the helper, in the middle of the train or infront of the caboose? Which is the best place to go to get trackplans and scale drawings etc over buildings? Their historical societies?