The only thing I would change from those plans i posted a few years ago would be to have the secondary air feed pipe enter not above the grate through the coalbed, but rather above the front door and go straight across to the hollow baffle;
But I thought that when you dump a bucket of coal on an old coal bed, you would need the secondary pipe laying in the bottom of the coal bed next to hot coals to get the secondary air hot enough to burn the volatiles. With the pipe suspended 6" or more above a fresh, black coal bed, wouldn't your temps cool so much that you'd be unable to ignite the volatiles that accumulate over a smoldering coal bed?
I like the idea of avoiding the pipe in the coals due to corrosion, but I'm just not sure it would work. I can see it working well with wood though.
If you can convince me that raising the secondary pipe would still burn the volatiles from the coal, I'd modify my homemade hand-fed in short order to get a cleaner burn.