On the '65+ 383s, 400s, 413s, 426Ws, and 440s, the ground cable from the battery to the engine block went from the negative post on the battery (Group 24 o4 27, NOT 24F or 27F) to the front intake manifold bolt on the driver's side of the intake manifold. A/C or non a/c. Make sure the metal on the throttle spring bracket and any related flat washers are clean (not painted) as the engine was painted with that cable attached, which explains the engine paint for about 9"-12" on the engine end of the original cable, when produced. The better those contact surfaces are at passing electricity through them the better the electrical system on the car might work.
Enjoy!
CBODY67