Look at the image you posted that ends in the number 22003. The bottom inside post, next to the valve cover rail needs 12 Volts. The inside post above it is for a tach.
Make sure the tach is compatible with electronic ignitions.
Make sure the 12 V from the ignition has 12 V in both "Start" and "Run" positions.

ALERT !!!!

That HEI with the stock coil will use less than 2 Amps.
That isn't a 10 gauge wire that they used. It's a skinny 13 or a fat 14 gauge with extra thick insulation.

'67 GMC 3/4 292 4spd