Hi Tim; Welcome to Permies!
Congratulations on scoring a new stove! Just as it is, it would work well in your shop building.
Your thoughts on trying to make it a RMH are a little outside the box.
I have my doubts how well it might work for you. The principle of a rmh, that enables it to push 50' horizontal. Is it runs Hot, Really hot, wide open roaring hot... With a thermostatic stove the air will shut off and the flow horizontal will stall ... and then it flows backwards... lots of smoke in your shop (hopefully no flames though). Or maybe it just smothers out , Causing ... YUP lots of creosote! The fire causing kind that a normal rmh burns up.
Now you might make it work using lets say 2 55 gal barrels. One with an inlet and outlet cut into the lower side and the other barrel enters low on the side and exits out the top to your chimney.
Both barrels
should have removable lids so they can be filled with heavy steel /
cast iron / granite boulders... as long as the air can freely move thru, the mass will heat and you will get extra warmth in your shop.
On your thoughts about pellets. Yes, some have managed to successfully build a hopper to
feed pellets. One fellow with a
greenhouse has done it... he also had a fire in his early development that could have burned him out! (It didn't). So it can be done, but it is not recommended for a new RMH builder. Much better to build a tried design as a first build and then move into developing a Frankenstein
rocket mass heater.