I'm running a campaign right now in the world of Magnamund. You can read about it in my story hour (although sadly, not that much of the Magnamund flavor comes through in the story hour).
If you're going to run a D&D campaign in Magnamund, you need as much source material as you can get. In case you didn't already know, you can read the text of the gamebooks at
Project Aon. (Of course if you still own your gamebooks you can read those instead.

) You will also want to check out two of the original Lone Wolf fan sites, Julian Egelstaff's
Kai Monastery and
Desert Lynx's Oasis.
If you have (or can somehow acquire) a copy of The Magnamund Companion, it is an excellent sourcebook for your campaign.
I also think that having the
maps from all the gamebooks would be nice for your players.
As for Mongoose's d20 Lone Wolf game, I'll probably buy it. I must've spent hundreds of dollars over the years on LW stuff, so what's another thirty bucks, right?