broken off spark plugs

Heres my story, I have a 95 4x4 in great condition bodywise. It only has 50,000 miles. However, it used to be a ski resort truck and they spread salt with it. Now everywhere underneath is rusting out...Motor too. Tried to take plugs out and 3 of them came out with the treads still inside, one other one is so rusted it only spins. Any suggestions on this or should I plan on replacing the heads?

Heres my story, I have a 95 4x4 in great condition bodywise. It only has 50,000 miles. However, it used to be a ski resort truck and they spread salt with it. Now everywhere underneath is rusting out...Motor too. Tried to take plugs out and 3 of them came out with the treads still inside, one other one is so rusted it only spins. Any suggestions on this or should I plan on replacing the heads?i have been able to heat,very carefully with extinguisher handy,and use an easy out bit to turn them out.