The 8-3/8 ring gear is used in Dakota (for sure, maybe others, too) applications of the 8-1/4... it's only 1/8" larger diameter, and is a direct bolt in. I think the 741 case also uses an 8-3/8" ring gear, but I'm not 100% sure on that.

The 2.45:1 gear set has it's own sure grip unit. The pinion gear gets HUGE on really low numerical gears, and the 2.45 is about as bad as it gets. TO keep any ring gear strength, they had to offset the ring gear a bit more away from the pinion gear so they could make the ring gear thicker. The 2.45 sure grip will only work with the 2.45 gear set. I guess you could use a spacer if you had to, but who makes those?

Clair