2002 mk3 Smiths Fuel Gauge

[Slip101]

I purchased a Cobra that was built in 2002. I converted it to EFI and while changing the fuel pump I also switched out the sending unit to the corresponding 1988 mustang sending unit (22 ohms empty and approximately 145 ohms full). The gauge now reads empty. I have an invoice from Finish Line listing the gauge and a "Smiths fuel sender - COBRA OEM" I have no idea what this means. It appears that the ohms are different. I've done a little testing and the installed gauge seems to be working properly. Anyone have an idea of what sending unit I should be using? Or anything else I may be overlooking?