Late 356C's had electronic tachs from the factory. Here's a pic of the one I'm using in my split. Took a while to find in decent condition at a reasonable price, but a whole lot easier to deal with than the older mechanical ones.
Not that it helps you convert the one you have available...
![Wink](http://cal-look.no/lounge/Smileys/default/wink.gif)
Hmm that looks interesting - looks very similar to the one we have, you see my friend buys things THEN asks me questions
![Smiley](http://cal-look.no/lounge/Smileys/default/smiley.gif)