I'm running a 9" in my 66, but with a frame kit and 15x15" wheels, so no 'normalcy' there.
A couple of things to consider.:
In a 9" you can get big bearing (late) and small bearing (early mustang) rears.
furd has another drop in center section (think it's a 8.2" or 8.8" or something) don't be fooled hunting the swap meets and salvage yards.
Aftermarket axles.... you'll get a lot of opinions here, but Moser and Dutchman motorsports are the only two I'd consider for a "STREET" strip vehicle. On the street you wrap up the axle in two directions. On the track it is only being stressed in ONE direction. A drag axle is able to take more wrap-up of a sticky track and high HP. BUT, it can not take the working of being wraped up both forward AND reverse (like going around corners). Moser seems to have a alloy that is very resistant to street driving, and still takes the abuse of the track in a heavy hitter. If your running a 9" and ONLY on the street with a very occasional trip to the track, A company in Pacific NW called Dutchman Motorsports makes the best damn street/strip axle I've found (and I have a small pile of twisted splines and broken axles to judge,,, mostly Strange!) The Dutchmans alloy is perfect for a locker or posi on the street with sticky tires like the QT pro's or MT's.
Oh, and a small bearing 9" is limited to about 33 splines, where the big bearing you can go 40+. For most street / moderate bracket racing a 33 spline aftermarket axle will hold up fine. If you want the 'best' axle for a hard hitting chassis, Mark Williams is the name, but you better dig deep into the penny bank before you order.
There are a lot of web pages around that give the work sheet for ordering a aftermarket housing, or axles for any housing. I like the Alston page myself. They explain that you HAVE to have the tire/wheel combination IN PLACE, then you can measure for housing / axle length.
Here is a link to the Alston rear housing work sheet. It will give you picture of what all you need to know to put a rear under your truck. Once you know EVERYTHING you need to know to order a custom housing, it's easy to go out picking through cores to find something close....... enjoy
http://www.cachassisworks.com/worksh...structions.pdf