It's got drive by wire throttles and coil on plug ignition too. The 3.0's didn't have that, so whilst you could probably swap all the bits over and physically fit a 3.0, there isn't an engine management system that supports the 3.0 with DBW and there'd be nowhere to screw the coil packs on . Conversion back to manual throttle could turn into one hell of a project as all the wiring looms would be wrong. Maybe a 3.2 DBW engine management would work on a 3.0 engine, maybe not... Could put a 3.2 or 2.6 in, but there aren't as many around second hand.
There's something not right about that ad too. The car is advertised with a mileage, and the picture shows a dash with what looks like the correct mileage, and the engine's idling at 500 rpm. So did the engine sieze just as the seller had finished taking photos or what? Also, why has he chucked that nasty looking mat on the driver's side carpet? It looks terrible, so expect the carpet underneath to look worse. Stereo is in "safe" mode.
If it was really cheap and for someone willing to bide their time and wait for the bits to do it up, and take a bit of a risk, it could be a nice project, but it's a bit of an unknown quantity, IMHO.
Kevin