If you are talking about the small earth cable on the front bank (closest to radiator), that one was always attached to the coil of cylinder nr 1, or cylinder 3 as far as I remeber, but for the rear bank I've had no earth cable there
Those screws at the rear for the manifold have been missing since I've installed the new manifold about 1 year ago, although I've never had problems regarding those missing screws...