Another 99 Intrepid Engine question

First time on the forum and have already learned some great information about Intrepid engine problems. I have a 2.7l engine with 139000 miles. A week ago we had the battery replaced. The battery was dead. But the kicker, two days later, the engine stops completely as I am going down hill--approximately a 15 minute drive. I coast off to the side of the road and it will not turn over. I had it towed to a mechanic that I never use on reccommendation on my regular mechanic. He thought it was the fuel pump and he can't do the pump because of city regs. The guy who towed it in diagnosed fuel pump. I trust him as well since he does repairs for insurance companies in two states and I work with his wife. The mechanic who has the car said the engine went out. He said that he let it run 15 minutes on idle when the rod started knocking. I never heard a valve, rod, anything coming out of the engine when it quit on me. My regular mechanic said he went out and listened to it and it was a rod.

My question: can it possibly be a timing belt based on other responses from the forum? Should I be looking into other possible explainations :oops:?

Also, I have been told since then that the 2.7l engine was a throw-away--not built to last long. Can the 3.5l engine be interchanged without having to change the wiring and harnesses? Thank you in advance.