Hi Partner, welcome aboard!! I have the Clayton 1537G which I think is pretty near identical to yours. What devices do you have installed? Barometric damper or manual pipe damper? Manometer? All natural draft or is there a combustion blower installed? Anthracite is quite a bit different than wood or bituminous coal and have different characteristics. Firstly, I would advise not to burn bituminous together with the anthracite, it will complicate your attempts. You can use a kindling wood fire or some cowboy charcoal to get your anthracite lit. After getting a good kindling wood fire going, add coal in 2 inch layers. Let each layer ignite before putting more on. Repeat this until you build it up to the top of the fire bricks. It may take 80 pounds to fill it initially.. Heat output is controlled by combustion air coming in under the grates, not by how much coal is in the fire box.
These furnaces are fickle to burn anthracite in. It took me a few specific modifications to make my coal burning steady and predictable. I only lit mine once this year, haven't lost the fire yet. I get 24 hour burns during mild winter weather of 25-35 degrees outside (heating 2500 sq ft) without it loosing any heat output with only slicing and poking under the grates in between. So don't get discouraged if things don't go well at first. Some learning curve is required as well as finding a tending technique that keeps her happy.