Research continues as I find time, though that's always harder in the summertime. Nevertheless, with the help of fellow modelers and historians from the Frisco.org wesbite, I've been able to get some more information on Battenfeld Grease and the line's history. I updated the original post to reflect the new findings, plus created a Google Map to provide some spatial relation for the items discussed in these posts.
I'll continue researching the histories of the various industries in an attempt to frame a modeling period for the line. I've traditionally been interested in recreating the mid-to-late-1970s and much of the equipment I already own dates to that era. Industrial branch lines like these were in fast decline following the Staggers Act of 1980 that, through deregulation of railroads, allowed for making the case for abandonment easier. Also, many cities experienced a decline in the urban industrial fabric as companies either consolidated, moved to the suburbs or went out of business altogether.
That being said however, there are some plausible opportunities for stretching the modeling window a bit to include some industries that may have not survived into a particular era. I'm cautioning myself in this arena though, since modeling "too far out of the box" doesn't appeal to me -- forcing rail service upon something that's no longer economically feasible destroys the plausibility.
So I might consider modeling a decade in general, though, if I were to span the year 1980, I'd have to choose between orange-and-white (Frisco) and green-and-white (Burlington Northern). Or even a green patch over orange-and-white? Hmm...