Jamie - I wish I could just change the sensor. The newer ECM is programmed for the larger tooth count - it won't read the other reluctor. There is also a chance the camshaft timing wheel is also wrong (but I think GM/Isuzu left these the same) Stupid computers. Stupid me for not building it myself (although until 48hrs ago I didn't know there were different reluctor wheels either)
Paul - I now have a nice new downpipe all wrapped in thermo-tec (thanks to Jason)