Missing heater core hoses

I did a pressurized test on my 72 Newport, and I don't think that the heater core is bad, but I am still missing the hoses from the engine block, and the lever that cuts it off. Could I have direct hoses, or would coolant running through it all the time overheat something? I hope it doesn't really leak. I can live without air conditioning, but I plan on taking a long trip in march, and I just may need heat!
also, would a 69,70,71,or 73 heater core be interchangeable?
Author: Jon O.