I wouldn't worry about head gasket yet, the OP hasn't stated any history with the car, and it may have been replaced already anyway.

Just get a new radiator, Behr or Nissens ONLY (I personally like Nissens), do not get any aftermarket junk. I did it in the beginning and regretted it after replacing it 3 years later.

Coolant is Zerex G-05 -- again, don't get generic crap. Find the correct stuff and your water pump will last and perform better for longer, its tried and true.

Change the oil immediately, overheating causes additive packages to become extinct. Use 15-40 diesel oil such as Rotella-T 15-40, Delvac 15-40, Delo 15-40, I'm partial to Rotella-T and Delvac. The 86 103, unless changed under warranty, will probably still have the pre-hardened cam and it is susceptible to scoring and wear. The zinc additive is a must that is within the above oils!

If the worst has occured and the HG is gone, its not too difficult of a job if you leave everything alone other than the gasket. You don't have to mess with timing, even the belt tensioner you leave alone. Its straight forward if you have some experience wrenching.

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