Sheep? ("Mike's got a 60, Dave's got a 60, guess I need a 60")Or they got it as a package with a 60 front? easier to find? Who knows.
Your typical 60 housing is probably stronger, but I'd build the 9, since the slightly lower pinion won't be an issue. For the time being, find one with 31 spline shafts, and you'll be in better shape overall than the 60, and you're sure to find 5-lugs that will match with what's more commonly available in a front 44.
60's will mostly all be full width, whereas 9's came in all flavors.
Bottom line - removable third members rule. SOOO much easier to do ANYTHING. No worries about welding to cast if you go 4 link. No diff covers to leak...
