Help! Moroso ring and pinion

Helping a friend clean out his garage to sell a few parts.

Found this unopened box-Moroso ring & pinion part #8563.

He could not remember what he brought the gear for, did not want to open box until the last resort.

Thanks

 

My catalog says Chevy 12-bolt, 6.17:1

 

top of 4th by the end of the block!

 

Shit, you could leave in 4th.

 

OK, thanks.