I am going to take a different position.
If it is not too bad, you may be able to drive it.
When you refill cooling system, put in Bar's stop leak as directed. You will need more than one container - don't skimp. Let it heat up and pressurize the system, and leak should stop. Bar's is the only one I have had success with. I have not had any luck with the ones that look like oatmeal. All they did was clog up everything, including the radiator core tubes, and cause severe overheating.
Over the years, I have used it in many vehicles until I got time to do a proper repair. Head gaskets, heater core, even a leaking water pump! When I was working 6 days a week, I ran it for 2 years, about 60 miles a day until I got time to fix engine. It coats everything inside, so engine runs a bit warmer, and temp sensor will read lower than actual temp because it got coated.
After you replace head gasket, I would run a good cooling system flush thru it - Dupont used to make a good 2 part cleaner with Oxalic acid and neutralizer- don't know if they still do. With a truck that old, good idea to get sludge and scale out of system anyhow. Reduces possibility of hot spots and future issues. I also remove the temp sensor and clean it with steel wool to make sure it reads actual coolant temp.
Disclaimer:
This has been provided by an old geezer, based on his experiences. He could be wrong, so use it at your own risk.