upgrading the rear diff
 

I have a wrx type r v limited, comes with the close ratio non dccd gearbox and an R160 rear diff. My diff is leaking oil and looks a mess, plus i want an R180 diff, recently bought bigger hubs and will be buying the other parts too. Did the R180 come with different final drive ratio's? I presume the ratio for the r180 will have to match the R160 one that is coming off? Will the prop hve to be shortened?

thanks.

what markers on my old diff indicate its ratio?