All models have the same cam-shafts and CDI units, the changes were to the Inlet Rubbers, which are called "Insulator, Carburetor" by Honda.
Standard Inlet Rubbers, Part No: 16211-MS8-000
Market - Germany (Honda Area Code "G")
Engine Nos: RC31E-5000020 to 5008561 for 1988 and
Engine Nos: RC31E-5100006 to 5101907 for 1989.
Inlet Rubbers (called "Insulator, Carburetor" by Honda): 16211-MS8-610
Thanks I found it eventually, looking up exhaust pipes now if any other Honda bikes fit and various modifications and upgrades because il be doing a resto-mod style to mine down the lineChange the carb rubbers
Africa Twin RD03 XRV650 Engine Restriction Details