SE6A, are you sure it is a head gasket that is leaking? If there is any doubt, a compression test will confirm. At 42K miles, I doubt the top end or the heads NEED rebuilding. However, once you replace the head gasket and before you put things back together, run a compression and leak down test; the results will tell you the condition of the top end and, if within service limits, will save you the time and expense of an overhaul that may not be needed.
If you are careful, you do not have to remove the cylinder and replace the cylinder to case o-ring. If the head gasket is leaking, when you remove the head bolts the head should pop right off. As soon as the head is off, secure the cylinder to the case with some 1/2" PVC couplings to maintain the cylinder to case seal. If the head gasket is OEM, it may be stuck to the cylinder. Once secured, us a plastic gasket scraper to remove any remaining gasket pieces. Clean up the cylinder, blow any gasket pieces out of the cylinder, replace the head and torque to spec.
Now you can run the compression and leak down test to evaluate whether or not the top end and/or heads need attention which I suspect they don't. Put her all back together and call it good. If the compression and/or leak down test show that top end needs attention, you can address the issues and the only wasted time and cost was the time it took to R/R just the head and the cost of the gasket. JMHO.