Hi spc welcome to the forum. I have been waiting for someone to try to answer your questions but with no response yet, I'll give it a try.
We really need a photo of your raised hearth and current chimney/stove setup. A photo will save a lot of writing.
Your raised hearth, is it a few inches above the floor? Like an area paved with bricks?? It may be easiest to extend or enlarge the hearth area to accomodate a bigger stove.
Is the location an actual fireplace, or a non combustible wall with a chimney 'thimble' about 5' above the hearth?
There are some stoker stoves with top vent and side mounted hoppers, older Alaska units I thnk. I'm not sure about new units, I'd just contact all the current manufacturers of stoker stoves
Post us a photo here so we can help better.