How many hours does it take to remove and replace a 3.8 liter engine i

For a shop that does it on a consistent basis, I'd say 9 to 12 hrs. It's not just the engine, it's all the other bits.

Plus if you're being told you have a blown head gasket or cracked head get a second opinion. These are very durable long lasting engines but the intake manifold gaskets do fail. This can mimic the symptoms of a blown head gasket or cracked head. Hope that helps! Jim