Ultimately we need to know your Long Term Goals. It might have the SOHC with the timing chain issue. It might not.
It might still be a good investment if the engine blows up in a couple years, if the rust isn't too deep. Any way you look at it, there is a certain cost of ownership of an older vehicle and that cost rises if it's an SUV. We can tell you "odds" but it very much depends on the particular specimen of vehicle and what you pictured does not seem unusual for rust in your climate.
As for the crack potential, you really have to go there and check it out yourself and be ready to pass on it. Explorers aren't exactly rare. If it is an older owner who seems financially set, odds are higher they are selling it at good price, but if the seller does not seem so well off, question everything, including why it's being sold. I like to meet people at their residence when possible. How impressive that is, tells you something about their standards. If they don't upkeep the home they live in, how much were they going to upkeep a vehicle they're trying to get rid of besides make it shiny?