Speedometer cable adapter 36 Chevy

I'm working on a 36 Chevy LowCab truck and need an adapter or special cable to fit the speedometer. The square drive on the 36 speedometer is larger than the standard .104" drive on most cables. Does anyone make an adapter or special cable with the larger square end?

Thanks

 

id just get a regular cable and build up the one end. thinking maybe a stick welder on low voltage, then file back down to square. if worst comes to worst, use epoxy.