A friend of mine has placed a 93 LT1 with auto trans and 93 computer into his IROC. The car runs great but we have a small problem. The speedo on the car originally was apparently mechanically driven, or so he tells me. The 93 of course is electric. As such the computer has the requesite speed information that it needs to control the torque converter, cruise control, etc. All the other gauges are connected and working, just no speedo. If you remove the electric sending unit and install the factory speedo drive he can have a speedo but then the computer doesn't get the information it needs.

Is there any way to retain the factory mechanical speedo AND send the electrical signal to the ECM that it needs?