1. 742 and 489 case 8.75" gears have a LARGER pinion shaft diameter than a Dana 60.
http://www.moparts.org/Tech/Archive/axle/1.html2. New, nodular iron 489 and 742 8.75" castings with forged steel caps have been available for years.
http://www.doctordiff.com/8-3-4-nodular-iron-casting.html3. '57-'64 Olds/Pontiac rears are strong because of EQUALLY LARGE pinion shaft and pinion bearings, but MUCH LARGER 9.3" ring gear diameter.
4. The main reason 8.75" gears break is due to the fairly small ring gear size and fairly small tooth contact area. All else being equal, if an 8.75" third-member had a 9.3" ring gear, it would be on par with the GM version.
