Whistelnut you cannot burn soft coal in a inclined grate stoker. With the rough discription of the land i would venture to guess he is located in either WV,KY,OH, or eastern PA soft coal is a lot cheaper than hard coal.
There is a small greenhouse near me that heats one 50"x50" hot house and two 25"x50" hothouses with old stokers. I have only seen the setup in the big one its a old octopus furnace minus the sheet metal shroud and it has a iron fireman stoker that feeds it. They vent into what looks like 8" wellcasing.
If your customer is frugel then I would not steer him to a new unit. The only new made bit stoker I know of is made by willburt in Orrville Ohio they are about $7,000 new. However soft coal stokers come up once in a while on craigslist.
Pellets have a lot less heat in them then soft coal, and they burn a lot differently. Soft coal burns hot enough to melt the ash together and as a result the volume of ash is reduced a lot, pellets basicly make nothing but ash. So the removal of the waste is completly different. If you wanted to burn pellets in a underfed stoker it would need to have a rotating ring like the prill stoker stoves, but a setup like that would not work well for burning eastern bituminous because, the coke would fall off into the ashpan and not burn up.
Have you ever heard of the wiseway pellet stove? Pellet Stove uses no electricity!
It seems like that might be the way to go sense your customer has allready shelled out a pile for a pellet mill.