[Sirrotica]

The aftermarket has many choices for 9 inch housings because the used ones are so old at this point, rust and corrosion has taken a toll on OEM ones.

Oval track racers almost always put a 9 inch under their cars, because they're tough for what they weigh, have a ton of aftermarket support, and are a breeze to change ratios compared to a Salisbury design axle having a removable gear set. The ability to change gear ratios quickly is a must have for oval track racers, especially when running at more than one track. Unlike dragstrips, there is no common size for oval tracks, plus banking, and surfaces, necessitate different gearing.

The one in the picture is likely built on a new aftermarket housing, with mount provisions for an A body GM car. Most aftermarket housings have a drain, and a fill plug in the housing.

OEM ford housings were drained by breaking the seal at the gasket after removing the 3/8 inch nuts on the studs, and refilled through a plug at the rear of the housing. If it was just changing gear oil as routine maintenance, a suction gun could also be used to remove gear oil.

I've posted before that the 9 inch is the SBC of rear axles, huge aftermarket support, strong, and lighter than some other choices available. Also easy to work on without a bunch of specialty tools. If desired, you can get a full floater design aftermarket 9 inch, no lost wheels in case of a broken axle.

The more splines the axles have, the stronger the connection from the center section to the wheels, and less prone to breakage on the axle shaft ends. Ford used 28, and 31 spline. From memory I think you can get as high as 40 splined ends. There are also tons of options for rear disc brakes, caliper, rotor hats with interal drum emergency brakes, etc. on 9 inch axles.