When the factory put these engines together, the original head gaskets usually lasted for about 200,000 miles. I talked to someone whose original gasket only lasted 70,000 miles, but that is the exception. My 86 went 195,000, and is now at 265,000 on gasket #2, and still has the original piston rings and engine bearings. Usual causes for head gasket failure involve improper preparation. If the head is flat and smooth, and the head bolt holes in the block are clean and have no excessive oil or foreign material in them to prevent the bolts from being properly torqued, and the properly lubed bolts are tightened in the proper order to the proper torque values in several steps, you should expect your head gasket replacement to give you long service.