Unless you want to build a jig or hire someone who has one, you cannot.
The important stuff is
The centerline of the carrier bearings---which must line up with the axles, must project a straight line out to the center of the axle bearing mounts
The axle bearing mounts must NOT be "canted, in other words they must be square to the above centerline--which is imaginary without a jig
The dimensions must be correct in relation to the axles, I.E. You don't want at least one axle too long/ housing too short, putting end pressure on the axle/ bearing. (This of course mostly with "green" ball bearings. With original tapered bearings, you would not be able to set end play)
Obviously, you don't want it too short, short enough that the axle splines are barely engaged
THIS page:
http://forums.vintage-mustang.com/vintage-mustang-forum/613830-straighten-bent-9-ford-housing.html
is one of many you can Google which will give the idea. You obtain/ make bushings which fit in place of the carrier bearings, and fit "tight slip" on a precision bar that is --STRAIGHT-- and additional bushings which fit the axle bearing mounts.
The bar can be "full width" or "half width" in which you check one side at a time.