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Ding Ding Ding
Cass is right. I found a date on the ring gear last night. After checking the case for condition I remembered where this set came from.
These were removed from a 74 Snow Commando p/u that was nearly rusted in half. Took them out thinking there would be a posi unit there and instead ended up with the 3.91 open rear. The date on the ringear is 6/25/73.
I looked over the 741 case 3.91's as well last night.
Something I found that was interesting was the part # stamping on both sets of 3.91 gears in two different number cases.(741-489) was the same.
2070228 391-1 MS 291
Date on the ring gear in the 489 set was 6/25/73.
Date on the ring gear in the 741 set was 6/28/70.
Just thought it was strange...



Ring gears don't care what size the pinion stem is , the ring and pinion tooth count is still the same so both rears having the same part number is not strange.