Sending Unit from Rear Engine to Tach

Anyone have two of these gems or does anyone have a part number?

It's for an IO360D on my 1966 337A, going to a standard, original tach head for rear engine.

I'm pretty sure this is the problem. When you switch the rear engine to the front tach, no reading. When you switch the front engine to the rear tach, there is a reading.

Thanks,

Keven
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LAMBORGHINI V12