If you want a Typhoon, go to SyTy.net forums and start reading up. Now is a good time to buy one because prices are low for decent examples.
As with all S-series trucks, the suspensions wear out quick. Ball joints and idler arms are biggies. Another S Blazer problem is rust/rot on the rear of the roof where the hatch hinges bolt down. Make sure the cladding (ground effects) are all in good shape andfit well. Cladding is expensive and hard to find in nice shape. Some interior parts are SyTy specific, so make sure its all there.
For engines and drivelines, I would say get a stock unmolested truck. Modded trucks for sale are usually someones headache that couldnt get fixed. These trucks are tempermental. They like new cold plugs and newplug wires.They eat this stuff. Intercooler pumps go bad, and can create high IAT's and induce knock. Make sure it's working. Fuel supply was barely adequate when they were new, so most have Walbro 255's now. If it doesnt have one it probably needs one. Alot of the used trucks run bad because the vacuum lines are all shot. This makes a huge difference. My lines crumbled when I replaced them- with only 80k on the clock. The transmissions are the weak point. Some say stock SyTy's can break a good tranny. Alot of modded SyTy's are breaking seriously beefed 700's, and are now going 4L80e.
I drive my 93 Ty daily since my Nova tranny is screwed up and I still love it after well over a year of ownership.