$600 for 87k? Thats a steal no matter the state of the power plant. I agree with all above.
But are we sure its a head gasket. It probably is, but I have read about so few actually going. It seems more often than not this little scenario plays out:
The oil filter adapter gasket leaks, this causes two things. First you can get oil in the coolant which can be seen in the reservoir tank. Generally this is a sign, on most cars, that the a head gasket is blow or a 90 year old lady put oil directly into the tank and washer fluid in the gas... Anyway, its happens like it did in my 95. Mechanic says blow head gasket after seeing that. To make it worse, the gasket can leak enough to let air into the water system as it cools (coolant shrinks when cooling, pulls air in) and eventually you get enough air in the crossover tube to cause high temperatures or overheating.
I dont want to get your hopes up. But for $600 you could walk away with a perfectly fine car after replacing a $30 gasket. If its not it, you find a cheap engine and plop that sucker in and still walk away with a good deal.