How hard is it to change ratios in an 8-3/4"?

"totally different housing, innards do not exchange from dana to 8 3/4."

Sabre67, what you say is correct insofar as the currently available parts are concerned, but long ago, before Chrysler adopted the clutch-actuated Sure Grip posi, Dana made a special posi diff (the "Power-Lock" or "Power-Lok", not sure) for the Chrysler 8-3/4" rear end, and it did come in a 3.73 ratio because that's what all the hot rodders used back then. Chrysler stopped using it when they went to the Sure Grip, but until then it was the only 8-3/4" posi diff that the factory offered. I'm not sure whether the Power Lock or the Sure Grip is better, but the Power Lock is certainly no slacker. I picked up a 3.73 center section NOS in 2003. It is not clutch-actuated like the Sure Grip, but I forget exactly how it works at the moment. Maybe some of the more knowledgeable guys on here would want to discuss that.