Another 9 inch question for the experts

[67rstbkt]

I just picked up a 9 inch rear end in awesome shape for basically free and have some questions. I've determined that it came out of a later 70's F-100, so it's longer than I need, but has 31 spline axles. This will be for my non-tubbed 67 Firebird. The tag on the 9 inch reads WDM-CK
Here are my questions

1: What should I narrow to? Should I go to stock Firebird width ( I think it's 1" wider than the Camaro)? Should I go stock Camaro width? Or should I go shorter than stock?

2: I will be running disc brakes, does this make a difference?

Any general pointers/suggestions?

Thanks