Mustang 8.8 rears are 4 link, coil sprung. Which means you need to put leaf spring perches on them.

As for width, I am sure someone on the internet measured on once and posted the numbers somewhere.

http://www.hotrod.com/articles/ford-8-8-rear-end/

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.