First of all, try not to bump your threads. It's not against the rules, but it is generally not appreciated.
Second of all, it is
strongly recommended that you install A9LH on the second 2DS. But that's not what you're here for, is it? Anyway, to install OOT3DHax on the second 2DS, you first need to set up the "Tubehax" DNS on the 2DS. This will block the browser nag. Next, you must use browserhax to access the Homebrew Launcher. Do this by downloading "starter.zip" from
here, and extract all the files onto the root of your SD card later. I ask you to extract all the files because you'll need them for OOT3DHax later. Insert the SD card into your 3DS, and run browserhax by clearing all history/cookies/data from the 3DS browser and navigating to this URL:
http://yls8.mtheall.com/3dsbrowserhax_auto.php
From the HBL, simply load the OOT3DHax installer (don't remember what it looks like) with your OOT3D game inserted, and it should install automatically. But you could just install Menuhax anyway, so what's the point?
The installer is included in starter.zip. Just run it on your A9LH 2DS and choose the version of your unhacked 2DS when installing.
They may have a different firmware on their A9LH 2DS. I'm fairly sure OOT3DHax is firmware dependent. If not, then your solution is much better than mine!