I know Dave by London has a hood tach on his white 69 2+2 4 speed. It'll be straight in front of the steering column, you just need to determine how far ahead on the hood. I suspect his was dealer installed as the metal work on the back side of the hood wasn't the neatest.
In 69 the hood tach was only offered factory installed on GTO, LeMans and Firebird. Of course the dealer or anybody could slap one on any car. Even factory literature shows a 69 GRand Prix with a hood tach but it wasn't offered by the factory.