Axle housing width

[Chev Korbin]

So I have a few question for anyone,.. everyone. What's the optimal way of deciding axle housing width? I know there are a lot of dependancies but the way I see it, in general you have wheels you want to run and and you have them mocked up on your project and you build the housing accordingly. Or you have a fabricated housing and you pick components that all work together to fit, i.e. wheels, bodywork, tires, etc. For those of you who have built your fair share of cars, how did you go about deciding that? For those of you tracking or auto-crossing your vehicle, how did you decide and is there an optimal rear track width that one should consider when choosing housing width?? I realize that optimal track width is going to be generally dependent on the manufacturer but, say for Camaros or Mustangs of the same year,. say "..all the '67 mustang guys are running this width or that width, and all the Camaro guys are running this..." does that make sense?
I have not ever had the opportunity to blueprint or build a solid axle, but I will soon be needing to acquire parts and brackets and decide how I am going to go about this new project. I would like to hear what other people have done and why you chose to do it one way or the other and how it worked out. Or if there is some other aspect that you build a solid stick around, please share. I have done a lot of homework already on the specifics of geometry and dynamic aspects of the rear axle as it articulates and what not, but I did not find a whole lot on axle housing width beyond lists of what vehicles came with what. I think this is one of those "...ways to skin a cat" subjects, but i'm hoping people are willing to share there methods and why.
Appreciate everyones input and thanks ahead of time!