64 Dart ground set up

The original grounding from battery to body was marginal back then. It is wise to add a big one from block to body. Buy a Ford style starter cable (eyelet to eyelet) and go from block to firewall. An easy way is one of the master cylinder studs. I know of no other big solid bolts through the firewall, but you could certainly bore and and add a nut/ bolt, use star lock washers.