There may be an adapter that can work if it actually works. So many don't. Maybe someone that restores them and update it to use electronic ignition.

I got mine from the parts place. It works with petronix.

Here is the one I got
http://www.ebay.com/itm/1968-Pontiac-GTO-LeMans-Firebird-Hood-Tach-5100-RPM-/350334392737?fits=Year%3A1968%7CModel%3AFirebird&hash=item51918e99a1&vxp=mtr