If you want the challenge, then go for it!! It will be a doozey of a challenge!
. I was just sharing my experiences, didn't want you to have erroneous information.
The problem with boilers, especially bituminous boilers, is that they aren't very effecient, about 50% after a week of burning and the surfaces get insulated by the soot throughout the heat exchanger. Make sure you have in your plan to open all the cleanout doors and vacuum/sweep the surfaces of the heat exchanger every week.
My boiler would get by on 200# for a few days, then gradually work up to more than 300 to keep the water at 150*, then I'd have to wheel out the stoker [just shut it off, the fire goes out in an hour or so with no air] The open the clean out doors and scrape the soot and vacuum it up. then back to the same process for the next week or two.
With anthracite there is fly ash, it is heavy, and settles on lower surfaces and if adheres to vertical surfaces, it falls off after it gets to a certain thickness, sort of self cleaning.
Switching fuels is easy, just add what you want to the coal feed hopper. not a big deal at all. And shoveling coal into the firebox is tougher than dumping it into the feed hopper with either an auger or 5 gal. buckets. I can wheel out my stoker, reinstall the hand fire grates, and have it ready to start a hand load fire in about 20 minutes. No need to let it cool, or worry about the fire in the stoker's firepot, it is going out, no air, just glowing embers for less than an hour.
As for hand loading bituminous: When you toss fresh bituminous on a fire, the volitiles immediately start to gass off, and unless you have a draft like .1-.2, you will get the black soot back in your face and into the room. You would have to make a conveyor to feed the fire with hot oxygen rich air blown into the volitiles to burn them off as the fresh coal is fed to the fire... an interesting challenge.
What I did was to open up the air supply, get the chimney really drawing, have 2-3 buckets of bitum coal at the ready. Shake down the fire, inspect it to make sure it was nice and hot. Then toss on the 100+ # of coal, and close the door QUICK !! Because the coal was going to gass off real quick. I also had to learn to leave a corner of the fire open, I used a garden hoe to open the fresh coal up down to the hot coals, otherwise the volitiles would build up, with not enough heat or an open flame to ignite them, Then the whole boiler would fill up with volitiles, and when the ignition finally occured, it would be spectacular,,, It kept my chimney clean !! looked like a Locomotive! and it also blew the flue pipes off a couple of times. Not a good thing... I had to powerwash the interior of my boiler building the next summer !!
From my perspective, I'd use the old boiler [sounds neat, and capable] and adapt an underfeed stoker, on wheels, so you could pull it out to service, clean or convert to hand feed. Then see how much heat you can make, and see about storing it.. A series of 250 gallon tanks plumbed in series as a storage unit, heating the basement would work. And prove the theory of heat storage without building the addition to the house with the built in tanks untill it is a proved setup.
My Dad and I spent a lot of time and effort on our heat storage system, but upkeep became too much work, we put in a wood burning hot air furnace... later propane, then we installed a new owner for the 'vacation house'.
A bit of learned knowledge about bituminous coal. It is sold usually two ways, 'run of the mine' and nut or stoker. The nut or stoker is washed, or sorted by size and is roughlly like pea to nut anthracite. With not very many fines in the coal. The 'run of the mine' is the coal just as it comes out of the mine, huge chunks like basket balls down to LOTS of powder-like fines. The fines are a disaster. The combustion air cannot get up through the fines, so they choke off a fire, get hot, swell, stick together into a gooey lump and make a bridge over the fire, often even putting out the fire. You have to go in after an hour and break up a bituminous fire, it has welded the pieces together into one sheet of coal, that is not burning well, there are few air passageways through the big lump of stuck together coal pieces. So you have to use a 'railroad bar' to jab at the big lump and break it up into smaller lumps so it will burn and not bridge/smother the fire below.
So if you go with a truck to buy bituminous PAY THE EXTRA for sized washed stoker or nut coal DON'T buy the run of the mine... like I did the first time..
The Beauty of anthracite is that each piece of coal stays independant from the next, and does not stick together, and will burn down to ash with little if any tending in a properly designed firebox [vertical sides, grates all across the entire floor of the firebox.].
Ok, by fingers are tired, and my coffee is cold.
gotta get something done..
I've attached a few photos, I think they are on the forum somewhere.