In my 66 c10 I just used the same ignition on wire that used to power the coil. Seems to work ok, been running for 3 years now with no problems. I once tried to put HEI in a 72 and found the firewall and cap had a space conflict. I didn't care about looks then and needed to get to work so used the hammer method to free up some space. Not recommended if you lose a motor mount though
........nofords