1998 Cadillac Deville replace head or entire engine

My 98 cad is blowing a lot of white smoke out the exhust and I lost a lot of water. The GM repair place said I had either a blown head gasket or cracked head. They informed me that it would be better to replace the engine because of problems with removing head bolts, etc.
Is this normal proceedure or can heads be successfully R&R?