Highlander: That's exactly what I was needding. You are probably right about the salvage stuff. Didn't know about the solid aluminum pusher block. Thanks for the input.
Jerry: I think you are right about the blower and air. In my handfed, I can have one side of the firebox completely dead due to going too long without loading. But as long as I get some of the new coal to catch, it soon spreads to the rest of the firebox. I definitely want to avoid a fire in the hopper. Seems like you'd want to have a variable speed control on the combustion fan to fine tune it.
I was also thinking that if you could get the pusher block of the Harman to stop it's stroke in the correct position each time (fully forward), you could effectively block the path to the hopper and avoid any chance of burnback. Not sure how you'd wire that to ensure that happens though. Might have to scrap the timer idea, or do some fancy ladder logic or something.
But I'm still thinking a setup like the Harman Magnum has the best chance of working with bituminous coal, due to its somewhat underfed design. And I think all the truly underfed stokers on the market are too ugly to set in my family room. Maybe I need to mount an underfed wil-burt or stokermatic pot in my stove body I built.
Thanks all for your help. I'll share all failures, experiments, successes, etc.