Now the fuel filter location is where ?
It should be between the fuel pump and the carburetor. Look for the hose that connects the two, and either a metal or plastic canister, maybe 2 or 3 inches long. I personally prefer the clear plastic ones, as you can see the condition of the filter. I used to buy them at swap meets for $1 each. They're easy to replace, just remove 2 clamps, remove the old filter from the hose, and reverse for installing the new one. Or at least, they should be easy to replace; sometimes, the filter was located behind the alternator, which complicated the job. If so, you can buy a length of fuel hose at a parts store (it should be 5/16"), and cut it so that the filter is in an easier spot for you to access. Depending on the condition of your hose, you might want to replace it anyway. I'm assuming a rubber hose; older Mopars had metal fuel lines, with 2-inch rubber hose connectors for the filter. Not sure what yours has. There should be an arrow on the filter indicating fuel flow; you'll want to install it with the arrow pointing to the carburetor.
Another thought; your earlier rough idling might have been due to bad gas. You reported that the car had been sitting for a year, which means that the gas had also been sitting for that long. Driving it around enough and refilling the tank may have cleared it out. You might also remove the gas cap and check the inside of the tube for rust. I hope you don't have it, but if you do, having the tank boiled out at a radiator shop is one option. If you do so, first remove the rubber grommet connecting the tube to the tank, as the acid will disintegrate it. The other option is replacing the tank with a new one, or one from a junkyard that's not rusted. Good luck finding either. Meanwhile, you might consider installing another gas filter before the fuel pump so that the rust doesn't damage the pump. You'll probably want to change the filters more frequently, and definitely use plastic filters so that you can see the condition. But if you don't have rust, none of these steps are necessary.
Regarding coolant, my Dakota had a slight leak, which I felt just below the hose connecting to the heater core. I tightened the screw clamp, which eliminated that problem. You report no leak at that location on your car, but you're obviously losing coolant somewhere. Is there any evidence of leaking coolant elsewhere? It might help to put a piece of cardboard on the garage floor under the engine when you park for the night (after running the heater), then check it in the morning. If it's dry, then I fear that Bob's right about the heater core needing replacement. If you tackle the job yourself after you receive the shop manual, it will be time-consuming. If you have a repair shop replace it, it will be costly.