1) A 3.5L engine conversion from a Pathfinder or QX4 to 02 Xterra 3.3 SE

[EXterror]

Any ideas what this would cost?

[Desert Rat]

A small fortune. There's been other threads on this topic - you might want to search for them.

In short, you'd need the entire wiring harness, ECU, the QX4 Transmission, custom engine mounts, a bigger radiator, custom exhaust manifolds and exhaust, and a lot of technical know how. It's been done (at Nissan), and it's a huge project.

The end result would be pretty sweet, but I'd consider dropping in an SC 3.3 with an underdrive pulley and better intake/exhaust first, as it would be a lot cheaper and easier, and the HP is close to the same.