18 spline aluminum case 4 speed

Im going to look at a 4 speed today and want to make sure that what I am reading in previous posts is correct. An 18 spline A833 was heavy duty stuff. This particular trans is an aluminum case. This doesnt seem as heavy duty as a cast iron, but I want to make sure such a thing exists and Im not looking at a weird unit. And as far as my reading tells me a 18 spline gearset isnt something that can be swapped into an OD unit?

Only numbers I can see on it are C95664 2

Thanks FABO!