has anyone had to replace a heater core in 1994 chrysler new yorker or car?

I guess I have several questions regarding the same thing about the heater core in my chrysler new yorker is this an easy job or will it take 7 hours like the mechanic says? I need to replace heater core in 1994 new yorker do I need to take out the whole dash what about the air bags will they explode on me if I dissaseble the dash to get at the heart core? Can I just put the two hoses from the heater core together and run the car with no heat to prevent damage to the engine? Is the heater core accessable without taking off the whole dash? Can I do this job myself?