Auto Parts: 98 Chevy Monte Carlo, chevy monte carlo, rocker arms

Question
I have a 1998 Chevy Monte Carlo and two days ago the oil filter fell off (Autozone provided incorrect filter) and the oil leaked out, leaving me driving it for about 2 mi without oil before realizing what happened. The car then stalled and I immediately pulled into a parking lot and called someone to bring me a new filter and oil. After replacing both the car makes a clacking noise that sounds like it is coming from the top rear end of the engine. We spent the whole next day (yesterday) taking the top end apart. While it was opened up we turned the engine over manually and all rocker arms and push rods appeared to be operating normally. Then we removed the lifter covers, took all the lifters apart and found and replaced two that were scored. Of course its not possible to start the engine with the whole top end apart (cuz that would be easy right =D) so after we put the whole thing back together come to find it still makes the same noise. I have gotten opinions from about 15 different mechanics most of them saying it may still be a lifter and the rest saying its a rod in the lower end. We are dropping the oil pan today to look at the rods and bearings in the lower end but I wanted to know if an expert has an opinion on what it is or if there are things we can do to test to determine what it is. Thank you

Answer
    Needless to say, driving around with no oil is not a good idea.  On the other hand, I have done it without damage to the engine.  If the noise is indeed coming from the top of the engine, then the lower end should be OK.  You need one of those automotive stethoscopes so that you can listen to each part of the engine separately.  Most stores sell one for less than $20.  I had some experience with one of these engines making a top-end noise and it turned out to be a slightly bent valve.  And, it could still be a lifter, as well.  If it was my car, and I planned on keeping it, I would replace all the lifters, pushrods, and rocker arms, being careful to lube them well first.  If the noise didn't go away, I would pull the heads and check the straightness of all the valves.  If all of that works, then it almost has to be a bearing, either rod or main.  By this time I'd be so far into it, money wise, that I would buy a crank kit and install it.  Sometimes you get a noise like this and it lasts 50,000 miles, there's no certainty that something is actually wrong (except that you drove it without oil).