I personally have done what some would call extensive research into this subject and can tell you that there are more then a couple of manufacturers of these units.
They are not at all limited to Japan. They are worldwide and many are not accessible to our US markets at all. They are made for just about any kind of three or four wheeled vehicle you can think of that needs to be steered.
Generally speaking what we see here in the US is very limited offering to what is available worldwide. However, what I found is that in my case new manufacturers, with few if any exceptions do not sell, or will not sell just one unit to you. Most you need to purchase in batches. Some as little as 10 or 12 but most in the 100 units at a time range.
So that if you are a custom builder, applying an EPS to your one specific application, you are really kind of limited to finding a used one and making it fit if possible.
Most of what is available here in North America is too big to fit into a Pantera. I had to go to the UK to find one and at that, needed to source it from a right hand drive vehicle, a Toyota Yaris, so that the motor was located on the left side of the column. The US version of that vehicle is as expected, left hand drive. The right hand drive was exactly the opposite configuration.
I personally have "built" three EPS units and was able to sell two that were too large to fit to "street rodders" where there was much more room under the dash for them to fit.
The electrical installation is actually quite simple and straight forward. Controllers are available from Bruno Antunes in Portugal @Brunossteering.com.
Unless you have the time and energy available to screw around with these systems, which most will not, I'd suggest that you consider using one of these already "re-engineered" kits. When it comes down to the value of your time and correcting the mistakes that you made, their price is really a bargain. That work has already been done by the sellers and you do not want to hack up your Pantera needlessly.