Hondata

I have searched the forum and still can get a positive answer if the s300 will work in a jdm P73 ecu from a 1998 jdm ITR.

Anyone know if it will work?

No

To use a Hondata system, you will need to use a compatible OBD1 ecu from the list at http://www.hondata.com/ecus.html . You can then use the Hondata s100 or s300 depending on what options you want ( http://www.hondata.com/sproducts.html ). I would recommend the s300.