Bit curious about Takanami...

[Vuki]

Is there any "other" content with Makoto Takanami that isn't from GTB or GT1? (I think it's GT1).

[JG]

VIPER Paradice & Lingerie games.  Typing VIPER.  Some art books and CG compilations.  The V-5 Manga. 
See http://www.sognadigitalmuseum.com/characters/rise/makoto.html for a full list of her appearances.

There's also a scene of her in workout clothes in the GT1 demo that was cut from the final game.

Plus, theres some doujinshi she shows up in, but all of that is fan work.

[Vuki]

I think I recall seeing a Nightmare Express edition that was Viper based. I'm pretty sure she was in that...

I'll do some searching, thanks.

[JG]

Yes, thats one doujinshi - I couldn't possibly list all the ones I've seen from memory.  You can always search for terms like VIPER on e-hentai and she'll show up in a few.