I found several grounds when I pulled my engine. One went from the head to the firewall, another from the Neg battery terminal to the passenger motor mount, and another from the starter to the frame. There where probably more as well.
The primary one is the Negative to motor mount. The one from the starter to frame is very important too. Ask me how I know, goo dgrounds are essential, burned up two starters due to corroded ground wires on my 40.
The one on the head, must just make sure the head is truely grounded so the temps sensor will work I guess, could be a chance it won't ground through the head gasket or something.
Traditionally one to the engine and frame was all a vehicle had, more is better.