The front of the furnace itself is easily removed by undoing the 2 screw that are tab mouted on the left and right sides.
If the furnace is original, the smell could be the exaust tube to the outside world failing. This would be very dangerous if it is the case, as you can get co2 poisoning real fast. For a couple of years they used rubber tubes and they were a weak spot.
The furnace is usally held to the floor with 2 screws that are accessable once you pull the front cover. The center screw in the outside plate is one of the attachment points, the screw goes on forever. The 4 outer screws on the outside hold the outer plate to the skin.
3 screws, power and gas disconnect and it should come out.
You may have to work it a bit if the tubes are all metal as they tend to rust together, but if they are rubber it will come out eaiser. Good Luck.