Welcome to the forum! Do you already have the Hyfire or should you be looking at an actual furnace with the blower size needed to circulate heat through the duct?
I have seen stoves tied into both supply and returns that have worked and that have not worked well. It is very dependent on the house, duct, stove, blower, etc.
Just curious what area are you located, I am wondering what kind of heat load you have to deal with.
Have you worked out the logistics of getting the tons of coal to the stove? That may influence your decision to use the existing thimble.
Pictures of the duct layout in the basement may help.