Unknown Johnson 20 hp outboard ?

I bought this motor with a 14 ft alumicraft and cant seem to find anything on the motor to ID. The plate is missing on the mount. The motor and lower unit is dark green with a white cowl which was painted over with camo green , when sanding the cowl I discovered that it is Johnson Sea horse 20hp. We found some info somewhere saying that locating the numbers under the transom vice would lead us in the right direction. they lied!!! Another source was to find the numbers on the silver welsh plug at the backside of the motor, I bet you know how that went.! If someone could please help me out here I really need it .(numbers found under vice, 315479),(numbers found under steering handle,E377630),(numbers under the pivet mountto vice,315430),(numbers found on small round,silver plug at rear side of motor,I asume is the welsh plug, J3245104). I would really like to confirm the hp , make, model, and the year if this is possible.Thanks, Billy R. Culver

I believe that I've narrowed it down to a 1975 or 76 by looking at the parts section and comparing the engine cowl.But, I'm not real sure if I'm on the right track. Billy R. Culver

Without the model nub mer the approach you have take by matching th cowl is the second best way