Need some advice on a possible buy. 3.4l/sc/4x4

The 3.4 is stout, even supercharged. It's damn near bulletproof. Nothing wrong with a supercharged 5vz at all.

That said, the supercharger alone typically leads to high gear, low RPM leanout under hard accelleration. Which in turn means, pinging...loud and audible. The factory ECU only allows for 7* of timing retard, which frankly is not enough in the situation I described above (or if the previous owner used anything but premium gas).

There's a couple of ways to help with the problem. 1 step cooler spark plugs and only premium fuel can help. This helps, but didn't solve the problem with my truck. I ended up getting a URD 7th injector kit and it solved everything.

It's hard to check for detonation results without a teardown to inspect. Doing a compression check is really all you can do.
Find out if the truck has a 7th injector kit.
Pull the plugs and see what plugs are in it and if they are 1 step cooler than factory.
Check the SC nose pulley for any play.
Test drive it. Get the truck it in the high gear (4th gear for auto, 5th for manual), low RPM (under 1500 rpm). If it's a manual, keep it in 5th and stomp the skinny pedal all the way down. If it's an auto, give it as much gas as you can so it doesn't downshift into 3rd. Driving up a hill helps put it in that scenario. Listen for what sounds like marbles getting shaken in a tin can. If you hear it...walk away. No telling how long the previous owner's been driving it like that.

 

Awesome. Don't be scared of it then. I'd slap on a supercharger to a 5vz with 200k miles without even flinching.
I beat the everloving shit out of my truck, redline it to death in the desert and it's still running like a raped ape.