what hp can a 742 case 8 3/4 handle

The 742 case is stronger, has beefier bearing caps. 489 has beefier pinion.

No it's not.

http://www.hotrodders.com/forum/how-identify-mopar-differential-191378.html

http://www.moparfins.com/Repairs/8-3-4_Rebuilding/Information_on_Mopar_Rears.htm

http://www.mymopar.com/Mopar8_75RearEndGuide.htm

I can keep posting links all night on it. Not that it really matters because they all three are very close in strength. It's a retard arguement, but the 489 case wins because of the pinion diameter. End of story.