If you are a paying member of Trainorders, there was a nice detailed series of post by someone over there that built an operating version of the Premier Elkhorn floodloader at Myra, Ky (CSX). You would need to search the archives to access these post. From what I remember, the outlet (chute) was controlled by a gearhead motor driving a shaft rotating inside a tube. The tube was milled open over the chute and the shaft was mill with a flat spot to line up with the opening in the tube. The structure above was a bin holding plastic pellets. As the gearhead motor rotated the shaft, a measured amount of coal would be dispensed per each rotation or it could be jogged 90 degrees off the close position and the pleets could drop freely through the opening. His comments were this usually caused jams and dispensing worked better by letting the motor rotate to dispense a set amount of pellets with each revolution. Personally, if I were to do this, I would use a chute with a sliding trap door controlled by a stall switch machine. Real tipples use this setup except the sliding outlet door is driven by compressed air. To load, slide the door open, the slide closed to stop the flow. Use the remote mounting hardware with the cable to remote mount the switch machine. The cable could be painted to look like conduit for power running into the tipple.
I've never seen anyone do an operating conveyor that works. Most belts are 48 inch max and it would be too hard to get a flex material that width in HO scale to form a "V" to conform to the required angled rollers. Anything that small with enough friction to be roller driven would need to be stretched tight and the surface would be flat allowing the coal material to fall off the sides when moving. There would be ways to overcome this but your conveyor would look nothing like a scale conveyor. The option here is to use a 1" diameter PVC pipe to represent the enclosed dust shields used around conveyors. Inside you would place an auger spun by a geared motor such that the pellets of coal would be augered up through he PVC pipe and fed into the loader holding bin. I've seen two done like this and they used big auger drill bits bought from Lowes and allowed to float inside the pipe.
In planning your layout, remember that NS only has a few hundred feet of mainline trackage in Eastern Kentucky. Everything else is just branchlines that cross over the Tug from the Pokey main in WV. There are no NS passing track in EKY, the branches are all single track except for under the many loaders. The Wolf Creek Branch in Martin Co. would be the best one to model as it does have small yards Martikki and Pontikki where you could tie a train up for a meet.
