70GMCer
Below is a link to the M&H wiring harness catalog for Chevy trucks. Go to page 28. That's where the #39695 tach w/ HEI harness is listed. I believe there's a little more to the harness than a length of wire with two spade connectors. I'm pretty certain it has the two conductor "V" connector that goes to the tach and the correct connector to attach to your HEI dizzy. The other conductor should go to a switched 12VDC source I believe. Hope this helps.
Monty
http://www.wiringharness.com/PDFS/TR...hevy_Truck.pdf