When considering a coal boiler, we all try to calculate how much coal we will need based on past fuel consumption...but we often don't account for heating extra space around the boiler, taking longer showers, or keeping the house warmer. In this case, the effective heating load is probably double for the coal unit due to the garage and heat loss from the piping. Even if the Modine in the garage isn't being used, there is still a fair amount of heat coming off the boiler. Keystokers usually don't come with any insulation on the top of the boiler...I would insulate the top and any exposed piping.
A KB-8 is a serious boiler; nearly 75 gallons of water in the pressure vessel. I would reduce the timer to 3 or 4 pins every 15 minutes, and set it up to circulate on demand. If your piping is a couple feet below the surface, it should be fine. Remember, the colder it is outside the more the boiler will be running/circulating.
Do you have any pictures of the boiler and piping?