Yeah, the axle is a trouble spot. I run an F-Body 8.25" because it is about the same width as a '65-67 B-Body and it work well. But a stock A-Body axle of any size might have a problem with the +30 wheels.
I was kind of focused on the front setup and forgot about the rear axle until the end. But he isn't going to find a 17" Mustang wheel with less offset that I am aware of. And anything that has less offset isn't going to work as well in the front with a 245 tire.