Starting in 1970, the engine ground wire was part of the negative battery cable. There was a secondary(smaller) wire from the negative terminal on the battery to the radiator core support attached with a 1/4"-20 bolt, this was also the attaching point for the ground wire coming out of the forward light harness too.
In 1969 and earlier cars, the engine ground wire was located at the rear of the passenger side cylinder head at the last bolt between the intake manifold/head and attached to the firewall at one of the screws for the voltage regulator(non A/C cars) or one of the screws for the water valve(cars with A/C).
Sorry, don't have any pics handy.....
