gears for duster 8.25 help

I am wanting to find a 3.73 or equivelent for my 8.25 axle on 72 duster, which was donated from a 73 duster. I am only able to find 3.55 or 3.90's. Any thoughts on where to find them at? Also do ALL chrysler 8.25 ring & pinion swap out with each other or is there a certain carrier like a 8.75 does?

thanks