Hello BillyR. welcome to the forum.. Your Mark III is a popular and good stove The Harman handfed stoves are well made, and do a very good job burning anthracite coal.
The Mark series and SF series from Harman have two minor issues.. the first is the shaker grates,, they can easily be moved too far by the shaker handle, opening the gap between the grates wide enough for the entire load of fire and coal to drop into the ash pan.. The technique to prevent this to look through the loading door at a clean firebox, move the shaker handle back and forth and watch the grates.. use chalk or some other marker to mark the side of the stove just how far you can move the shaker handle without opening the grates too far. After you are used to the stove the mark can be rubbed off the stove..
The other minor issue is look at the front of the front grate. You can see that when the back of the grate has a large gap to the next grate, the front of the grate is against the front of the stove and the gap is much narrower.. What happens is when the stove is burning, and the operator shakes down the ash, the coal in the center portion of the firebox gets plenty of shaking action, and the air passageways to feed oxygen to the fire are restored.. But the front of the firebox tends to accumulate ash over the front grate, and this clogs the air passageways resulting in a dark, non burning section of coal.. The technique to fix this is to take one of those annoying political signs from the road side, and using the heavy metal wire frame from the sign, make a poker with a 90* 'L' bent on the end, the 'L' should be about 3" long.. buy going through the ashpan door, you use this poker to feel for the gaps in the front grate, and poke up from the bottom, a shower of ash will fall down opening the air passagways to the coal at the front of the firebox..
With the two techniques above,, a barometric damper [recommended by Harman, and most of the forum members] and a good chimney you are ready to enjoy a great hand-fed stove..
Hope this helps..