Lou is right on target with the connectors and the relays but I don't consider the Chassis a good ground. Also I have seen several cases of grounding to the block and through the motor plate cause electrical problems (trans brake solenoid, ignition miss, gauges etc)
I would suggest that you ground the battery to the starter ( I drill and tap a hole in mine
) and run a #8 or larger wire from there to a ground buss ( a piece of 1/4" thick brass or un-anodized aluminum) and ground everything important to it. This may seem like over kill but bad grounds can be the toughest things to locate/identify so why guess.
Just my 2 cents worth