Stockingfull will correct me if I'm wrong, but I'm pretty sure this style stoker has the grates hanging on short 2-3 link chains and the whole grate and motor/gearbox rocks fore and aft with the upper end receiving the fresh coal, and the ash dumping off the opposite end..
Jay gave me a stoker unit like this, it ended up becoming part of Matthaus' " History of Stoker Development Museum"
It is an interesting design, uses the force of gravity with a slight sliding or rocking motion of the grate to keep the coal moving down the grate to the ashpan.
Maybe Stokingfull can get us a photo of the side of the stoker showing the chains..??