I don't believe the factory gears were stamped high impact. Just the ordering changed, not the gears.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ss427copo</div><div class="ubbcode-body">Yup.....they sure were. Stamped high impact. </div></div>
Those don't appear to be the original gears. I see a date on the ring gear of 3 70.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bwag</div><div class="ubbcode-body">Jeff , Did you notice the date code on your broken pinion gear June 69 ? We had 4.56,4.88,5.13 and 5.38 gears in and out of the car over the years. The 4.88s seemed to be the best combo overall.Some of the gearsets we used were the hi impact gears. Bob </div></div>
I don't see a June date - I think that's the part #. Just a date on the ring gear of 3 70 (7 is hard to see) and maybe the same date on the pinion, but I can only see the month code (3).