I am no 6 bolt expert (i'm a 2g 7bolt guy
But according VFAQ
Note that the early oilpan flange is flat in the middle where circled (right under the crank sprocket). The late oilpan drops down in that area.
Note the early oilpan side bumps out towards you in the circled area, the late pan bumps in.
Your engine is a 6 bolt: