8 3/4 I.d.
Kevin, this is one of the better sites with complete rear-end information, as well brake setup requirements. All isn't as simple as just a new rear end until you read everything including...the depending transmission if auto 904/727, driveshaft length, Axle width ect..Also in this link should talk about your brake shoe application. I take it your happy going from a 7.25???
Of course after your read ask more questions if required.
http://www.autohobbydigest.com/8_75.html