You can put an aw4 into it if you find one with a 4.0l. it is a little work swapping and welding but doable. Without knowing what you are dealing with it is impossible to figure cost. Miles should come into play on deciding wether you should just do a bearing swap. There was a marine on here Kelti who just dropped the pan and popped in all the bearings and drove the thing into the ground until he snapped the frame. To isolate the noise you need a stethiscope or a long piece of metal like and extension or big screwdriver.
There are a bunch of possibilities for noise. Oil pump, timing chain distributor bearing. Try and isolate it down. I am not saying it isnt the engine itself but the 2.5 and 4.0l are both great engines and regularly get more 250,000. I am going to PM you a member here on the forum. He is in Hawaii. He might be able to direct you to some parts when you figure out where the noise is coming from.