Not trying to give you bad news...but almost everything you are doing is going to be custom. been around this forum for 11 years, and not sure i've ever seen someone finish a full FSZE obd-I conversion without some very major things...that they simply gave up on later...
First...try to find a factory service manual for an FS-ZE equipped car...it will no doubt be in japanese, so after you get it...find someone that can help you translate it. I'm not kidding about that, you need to know all kinds of information about the sensors for the OBD-I ecu...its very unlikely that all your triggering sensors from the OBD II system will plug right in to your obd-I system...
also...do you just have the OBD-I ecu? or do you also have the harness?
I know you're probably already invested with this...but its just going to get more and more complicated from here out...the JDM cars use a different gauge cluster harness...you will have NO gauge information of any kind until you acquire or custom make that harness...
honestly...at least consider a standalone computer...and just sell off the JDM ecu. You'll be starting with a system that can adapt to your situation, as apposed to having an engine computer that is forcing you to use very specific sensors...that are impossible to find outside of Japan. It'll be another $1000, but you should be able to get a couple hundred for that ecu (OBD-I 2nd gen probe owners are always after them)...and you'll be starting from a much more realistic situation.