Forza Motorsport 4 V4 Title Update for NTSC-J.

You can find a few title updates for the game on http://xboxunity.net/ - I'm not sure any of those will be for the NTSC-J version of the game however.

Unfortunately you will probably find on English speaking Xbox websites PAL and NTSC-U makes up the vast majority of the content. I actually do have an NTSC-J Xbox 360, however don't have the NTSC-J version Forza 4 to get the update for you.

 

Am I right in presuming you have a legit version of the game (not burned) however can't go on Xbox Live for some reason?

What you linked to for changing the media ID should work if you have a Jtag / RGH hacked Xbox 360 as the title updates for most games are pretty much the same, discs from different regions have different media ID's so require the title update to have that media ID. For a non modified Xbox 360 you can't edit the title updates, as it breaks the signature, essentially meaning meaning the Xbox 360 will see it as corrupt.

 

If you update a RGH with a normal system update it will brick the console, however the Ethernet port is useful for playing system link games and copying content to the console over FTP, so that seems a bit of a strange thing to do. As you have an RGH i'd honestly try changing the media ID on one of the system updates you have found and see if that works for Forza 4.

 

That I'm not 100% sure of. I thought you'd linked to a tutorial on how to do that, however I see that is not the case.

Do you have access to a friends Xbox 360 you could just put the disc in and obtain the update?

Failing that as you have a RGH and own the game legally it might just be easier to acquire the PAL / NTSC-U version of the game. Most of the time the language / subtitle options on international releases such as Forza are identical between regions.