These 3 pages of the 1e DMG explain how to convert AD&D characters to Boot Hill and Gamma World and vice versa.
You admit it below, but I think I still need to say it. This is so far outside of what I would call "support" that it hardly bears mention. If anything, it is an explicit statement saying that if you want to combine D&D with the tropes of some other genre, you need to completely change setting via weird magical phenomenon and convert your characters over to a totally different ruleset. It is the exact opposite of what I would want to see.
Yes, you are right. D&D never directly supported bonzo Rifts like play but it certainly was not said that you couldn't add such to your D&D game should you choose to. (See also S3: Expedition to the Barrier Peaks.)
"Bonzo Rifts-like play"? That isn't what I would want to see at all. A somewhat broader definition of the word "fantasy", perhaps, but certainly not "bonzo". That can certainly be fun (I'm fond of many of the SaGa games), but it is far from the only way to mix things like guns, technology, and fantasy.
If you don't see the influence of D&D on Final Fantasy in all its forms, you don't know D&D as well as you might.
Well, certainly D&D has some small influence on even the most recent Final Fantasy games (they still have HP, Levels, and a generic group of loosely allied heroes on a quest, after all), but that is hardly the point.
Keep in mind, what you quoted was written in response to someone putting forward the idea that D&D can be seen by fans of modern fantasy as the defining pinnacle of the kind of fantasy they have been exposed to, because videogames primarily draw inspiration from D&D. That is simply untrue, and excessively dismisses the imagination and creativity of the countless games that have been made over the years. In terms of game mechanics, the Final Fantasy series abandoned some of the basic premises of D&D (important things like characters who have set classes) in the second iteration of the series, and never looked back. In terms of "fluff", presentation, and the like, recent Final Fantasy games don't resemble the "vanilla fantasy" of D&D in the least. Final Fantasy 12 probably takes more from Star Wars than it does D&D. As for the upcoming Final Fantasy 13, well, see for yourself...
[ame="http://www.youtube.com/watch?v=hDjkGUM7skk"]Final Fantasy XIII Trailer[/ame]
Not really a lot like D&D on any significant level. And this is from a series that started as a D&D clone. Countless other videogames started even further away from the D&D baseline, and diverged just as far. The Breath of Fire series, for example (I mention this one simply because Breath of Fire: Dragon Quarter has to be one of the most un-D&D-like fantasy games I have ever seen). Even though D&D may be the root of the genre, it doesn't define or embody the genre as a whole. It is the same for videogames as it is for tabletop RPGs, really, except that D&D isn't the giant gorilla of the videogame market like it is in the tabletop RPG market.
** Hey, remember when it called The Dragon.
???
The fact that your sentence is incomplete aside, I never read Dragon magazine, and 1E was before my time. Seriously, I wasn't even born yet when that was first printed.