PLEASE! I realize there's a lot of pride in ownership within this forum; but, before committing major cash, please consider either a Keystoker Koker, Alaska 140, or Leisure Line HyFire hot air furnace! Moving heat around a house is a major deal; and, you already have the problem basically solved with your existing oil system FHA duct work.
I ended up with a Keystoker Koker FHA thermostat controlled furnace (~160K btu), with cold air return and hot air supply plumbed into my existing FHA system---and I couldn't be happier. Using a single digital programmable thermostat and heating a two story ~4000 sq ft house, my indoor temperatures vary only 1-2 degrees throughout.
The only thing I'd change doing my project over again would be simply using ambient air for the Koker's convection air intake (the Koker comes with mini-filters for doing just this); and, plumb the hot air supply directly into my existing FHA cold air return, using the existing furnace convection/distribution fan to move the hot air around the house. Reason? The cost of running a simple verticle duct up to mate with the cold air return would have been significantly less. And I probably could have done the job myself; since, all the materials are readily available at Home Depot/Lowe's.
Please check out Leisure Line's web site. They have a nice diagram of how to make this work:http://www.leisurelinestoves.com/1904137.html
You'll need to keep your basement door cracked to supply a "secondary" cold air return path too... And run a wire from the coal furnace over to the existing furnace to turn on its convection fan to move your hot air around---easy stuff.
Don't go with a "tinker toy" solution. Either the Koker, 140, or HyFire will meet all your heating needs. The stokers can be adjusted to fine tune your heat requirements. And being stokers, you'll only need to service these furnaces once a day, filling up the coal hopper, and dumping the ashes. The only feedback I have for you here is the 140 has a relatively small hopper with respect to the capacity of the furnace. You might need to service a 140 twice a day in cold weather. With my Koker's 6 bag/240 lb hopper capacity, I've never had a problem running out of coal, even on the coldest, windiest days.
Don't forget about a hot water coil to solve your DHW needs too.