These motors are very similar to old school designs, cast iron block push rod engine, just fwd.
If you're positive you have rod knock it's probably just best to replace the bottom end, seems that's the consensus on the cheapest and easier way out.
But as far as the motor you have once it's running fine. The LIM gaskets are most notorious, of course if you tear it down and replace the bottom end or whatever you decide to do, you will have that covered just make sure you use the aluminum intake gaskets they are the 2nd design. Also with 142k miles it wouldn't hurt to get a new plenum (your upper intake manifold), it develops a leak near the EGR. Those are the two things that pop in my mind as far as risk factors on your 3.8. Tis a good motor otherwise.
I'm curious to see why you have rod knock. Good luck.
