The 4.5L I-6 does hold up extremely well. The engine was designed for durability and longevity in harsh conditions - the typical suburban soccer mom was not the design goal. Rather, use in Oz, Africa, South America was the target - so torque is available down low, redline is low, mpg is low. Some of the engines have had HG failures, but you'll have to spend a lot of time searching to find examples of bottom-end failure.

You won't go anywhere particularly quickly or inexpensively, but you will get to your destination.

190k on mine and it is very quiet and smooth and uses virtually no oil every 5k miles.