LW is a complete game, not just an add-on for D&D.
That said, it is based on 3.5 edition rules, and the difference between 2E and 3E is pretty huge. So, IMHO you have a lot of work to do if you want to convert it back to fit with old AD&D rules.
I recommend you try it as it is first. Then, if you don't like it, you can change it. I personally thought I was going to convert it to my game system (and I did actually convert the Kai Lord), but then I found the game in itself a very nice piece of work, so I decided to use it as it is. And the conversion I was going to make would have been way easier than the one you're planning for.