What is it? If that is a model for a condenser, you could take a stab at it being a 5 ton, based on the 060 in the model. ( 60,000 BTU)
If this is original, it is probably low SEER, and worn out after 28 years. This would be the time to condsider replacing it. Naturally, it will require replaciing the entire indoor unit ( cased coil, air handler, etc) because you cannot mismatch a new 13 SEER (minimum) with any existing equipment.
If that is just a gas furnace, I would guess 60,000 BTU input.
As far as the room addition, are you guessing at the requirements ( bad idea!) or will you have an HVAC contractor do a heat load calculation for you?