I'm all for being a smart ass, but at least come up with a resource that doesn't involve pirating copyrighted books off torrent sites before you get all RTFM on him.
As an aside, I don't think it's impossible to find those aforementioned legally available copies on torrent sites. That said, I didn't really even look at that link. I saw that there were torrent links at the beginning, but there were less suspicious looking ones below. Google is much faster at answering questions than we are, and surely a search for AD&D mechanics would have also quickly presented him with a vast array of information. I'm a big fan of being helpful, and that means more than just giving someone the information they want. The nice thing about LMGTFY is that it helps you teach people how easy it is to find things online.
For ROM, I found the best areas to use as "models" to be Copper's, Raff's and Hatchet's.
My advice as to thAC0 is, leave it alone. It works, it's linear (the only thing that is), and everything else depends on it. Sure, you can make radical changes to the combat by tweaking it a bit, but then you have to mess with everything else to get your balance back between your Newbies and your Heros. Let it be and play with the stuff on top of it.
I've been debating this same thing for quite some time. The way that I looked at it was to sit down and determine exactly what should take place during combat. Character A takes a swing at Character B - what steps occur during that split second? I wrote down what I figured a melee attack procedure should be and then whipped up a function to reflect that, kind of following along with what stock SMAUG had going. It turns out that the SMAUG function didn't work the way I imagined it so it got rewritten quite a bit. Take a look:
It was pretty easy to modify calls to it in the fight code. I only needed to add flags where they were necessary, namely for skills that call oneHit(). They can be flagged so they cannot miss, be evaded or blocked and such. It's sort of hackish (lol @ goto call) but it works the way I wanted and allows for spell effects to check various stages and such. Think melee shutdown skills that harm the attacker when they attack, regardless of a successful hit.