I don't have the answer to your question, but here are some SVX ECU resources I've found useful in the past:
Overview:
http://www.alcyone.org.uk/ssm/ecuinfo.html
List of different ROM images:
http://www.alcyone.org.uk/ssm/ecuroms.html
How to modify the ECU image:
http://www.alcyone.org.uk/ssm/ecumod.html
Hope it's useful.
Cheers,
Ian.