I'd take it back to em mate and say what's happening, i don't know whats involved in the conversion part to if that's caused it. Something worth looking into though (if the r33 is the same is my r32) is a cog in the gear box which goes to the speedo. If something has happend to that it might cause it. I had that cog break up causing me to only have 1st 2nd and reverse gears when it lodged the gear box up. I'm not a mechanic but it's just something that sprung to mind reading this.