I'm not sure if there is a way for SOHC's to disable the speed limiter. At least, it isn't documented. For info on the DOHC speed limit cut check
http://www.240sx.org ,
it's in the FAQ.
Maybe you can see if your ECU has the same wire color/stripe and position. If it doesn't have both, I wouldn't mess with it.
The other way to get rid of it would be the Apexi Rev/Speed meter. At least I've heard it intercepts the speed signal and disables the governor by "tricking" the ecu.