Hi Len,, it's summertime,, and 90% of the forum members are on the site only ocassionally,, so responses will be slow.
You want to pull cold air from upstairs into the coal furnace.. you don't want to pull cold air off the basement floor, this is the coldest air in your house,, and it will cost a lot more coal to heat this basement-floor air than warm air returned from upstairs..
Personally I would NOT direct vent [actually powervent] a coal appliance if you have a chimney.. the power vent MUST run all the time there is a fire, so with a coal unit this is 24/7... with oil, the power vent only needs to run when the oil burner is running,, which we hope will be almost never once the coal unit is installed.. So powervent the oil furnace,, chimney vent the coal furnace.
I still recommend hooking it in parallel to your oil FA unit, and using the ducts you have.. I'd do it right the first time,, 'cause it is so easy to 'just get by' and it may go that way for years... so I'd do it right the first time and then sit back and enjoy the heat...