Technical Can this Ford 9 inch work in my 31 Ford model a coupe project?

Maybe the Harley trike driveshaft turns the opposite direction so they flipped it over. The brake lines look kind of sloppy so could have been relocated along with the vent. Beside that, the oil fill plug would be wrong.

 

I can't help with the I.D. of the axle, but if you can come up with a 9" housing from a '57 Ford wagon, it will fit just fine. use a later center section as the '57 was a little weak. I am using one on my 29 Ford roadster project , and it fits fine. It will be using coil-overs on the rear. I had originally planed on using the buggy sprig, but changed my mind.

 

If the chunk can be left in original position and be bolted up to the reversed housing, it will work. Nobody does that, however. You really need the wheels and tires mounted and bolted to rearend to get proper clearances. Wheel offset, tire width, and rearend width all come into play.

 

That setup looks questionable.