Hey I have a series 6 rx7, and a series 7 engine with harness, I'm thinking this should work... Google Translate I wont be able to use a stock series 6 ECU will I?

The link is a knight sport ECU conversion.

 

If you look on Yahoo jp, they currently do 16 bit to 8 bit and 8 to 16 patch looms, they usually ask around 10,000 yen.

 

I have see this extension harness in the past and I want to buy it too.I dont think that will work correct and that because they didn't connect to electric load unit of 93 car ,99 spec have it in the ecu.
So first issue is that you dont have a working elu until you rewire it your self.
Second issue will be the egr solenoid on us spec fd and switching 2 on eu fd.Jdm versions have 7 solenoids not 8.
This adapter convert the 93 harness to fit to 99 spec ecu if you would like to use your ecu then you can use jdm engine but with your harness and vacuum rack.