Aftermarket wheels, 17" (maybe 18) BBP

Don't forget that a rear disk brake kit will add width as well. The drums are only like 1/16" thick at the axle flange while a disk is more like 1/4" at that location.

I've got a layout from years ago where I was trying to figure out what wheel and tire I could run and that layout shows 58" OA. It's been enough years that I am not sure where I got that number though. I will see if I can get a measurement off the 8.25" in my '73 in a couple of days.