Another welcome to the site Chuck. Sounds like a nice garage you got there. What do you do in it? Run a business, or a hobby work shop for cars, wood, or something else?
Me, my garage is a little smaller, and was heated with a Modine propane heater yrs ago. The price they get for "limited use" propane was insane. The heater went on the blitz almost 5 yrs ago, and I still haven't fixed it. It' has seriously cut down my motivation to go out and work, with a small kerosine heater, for hobby purposes, in the frigid cold. I only go out there for unscheduled maintenance.
Since I've begun burning coal in my house, 3 yrs ago, I thought of using a coal stove in my garage, but am worried about the effort keeping a coal stove running in the house, "and" in the garage. I also don't know much about the Gibralter stove, but if it's a combo stove, might be a good thing. If my garage was to see a projected job of only a days work, then I think a few logs would ignite quickly, and supply enuff heat for the day, without the need for the involved procedures, of firing up a new coal bed. (Someone can jump in and correct me if need be). If the job was to require a few days or more, then having the option of long burning coal might be more appealing. Just a thought. As for chimney placement, just keep it away from the work area, if you have the option. A neighbor of mine w/ a 2 car attached garage, put his woodstove right square in the middle of 1 bay, so now you can't even get a car in there.