Hello Mike, your specific mines and experiences burning those coals are greater than almost all of us on this forum combined.
I'd PM member 'berlin' he is located in the western PA western NY area and has lots of experience with the Bituminous coals available. Maybe he will post a list of mines, breakers and retailers for us.
What you describe about how the coal burns is typical Bituminous. For $90/ton, I'd borrow a truck and drive a few hours and get some Anthracite from the Pottsville area, about one hour northeast of Harrisburg, on I-81.
If you are home to tend a Bitum fire, and have a stove or other burning appliance that can handle the soot/bridging/ ash quantity, then finding the best mine to buy from is worthwhile.
Does your Clayton furnace have V shaped firebrick on the bottom/sides of the firebox?? or are the sides vertical.?? Vertical will make your life much easier for burning Bitum or any coal for that matter.
I'd PM Berlin, he's the bitum guru.