I have a 98 yukon with a 5.7l 350? My orignal problem was that it had a compression of 90 on #5 cylinder. Since then I have found I have a blown head gasket. It was recommended since I had another block(crate engine) to just swap them out. What all is recommended to change when doing this? I know the plugs, wires, rotor, d cap, coolant, and oil. Is it anything I missed? Also, I was told that some sensors may need to be changed. If so what are they? All I know the guy said something about temperature but he couldn't name the sensor. I want to get this right so please HELP!

The sensor he's referring to is the coolant temperature sensor (CTS) and, yes, that should be replaced with a new one.
And a new thermostat and radiator cap. Have the radiator tested for sufficient flow. A new water pump. Both radiator and heater hoses, and the drive belts.

You may want to consider a high output oil pump and perhaps install an oil cooler during this swap.

Ok Thanks for the help and just wondering why change the radiator cap?

Ok Thanks for the help and just wondering why change the radiator cap?
For the same reason the thermostat gets replaced: it gets weak over time and loses it's ability to seal and purge air properly.
It's a relatively inexpensive part and considering how vital it's function is, gives peace of mind knowing that the cooling system will be full and operating properly.