The Grand Trunk ran through the Dequinder Cut and out to Pontiac. Near where the Poletown Plant is now, another line branched off to Mt. Clemens paralleling Groesbeck [[this is the line that Thomas Edison worked on). I would guess the "Machinic Shop" was along one of these lines.

Since Grand Trunk was a Canadian railway, I wonder if Machinic is a Canadian term. So it could possibly be a shop in Canada. Here's their route map:

http://en.wikipedia.org/wiki/File:1885_GT.jpg

They had a ticket office on Woodward [[Foran's Pub), but I wouldn't think they'd have a shop there.