Welcome!!
I also have a Japanese Mustang and would be happy to help answer any specific questions you might have regarding these unique Mustangs. There are a number of unique parts that are very hard to find on these cars so I would suggest doing some research before you start tearing them apart. I'm looking for a piece off the power antenna so if you have some spare parts I'd really like to talk to you about it.
I'll send you a PM with some contacts of 71-73 Mustang owners in Japan who can probably help you out quite a bit.