[jspatz1]

One nice thing about bronze bushings, if your shafting doesn't quite fit, you can easily ream it out with a drill for an working fit.

As Dick said about D-shaft...you only need a setscrew flat in one spot so just grind that in, or drill a small crater with a drill point. Doesn't need to be precise. With bronze bushings, it would be best not to have the edges of a D-shaft turning in your bushings.

On tapping a setscrew hole...what I meant was that you can buy a tap (small cutting tool that turns a drilled hole into a tapped hole) and drill and tap a setscrew hole yourself. Easily done with a drill and vicegrips. Don't let lack of setscrew hole keep you from using a part that is otherwise perfect, you can add it.

Regarding the thrust bearing contacting the race of the flanged bearing...you do NOT want the thrust bearing resting on the inner race of the ball bearing. This would mean that the ball bearing is supporting the weight of the system, and the thrust bearing is doing nothing. The whole point of the thrust bearing is to bear the weight and keep side-load off of the inner race of the bearing. You want the thrust bearing supported by a stationary surface. Add a big washer under it if necessary to make it rest on the outer race or housing.

Yes, drill rod is perfectly good enough if it is cheaper for you. Note the tolerance to be sure it will go in the bearing.

As to whether stainless is necessary, that only depends on the environment it will be in. If it is outside, ground steel will rust pretty quickly. If you really want to avoid the expense of stainless, you can try to wax, oil, or clear-coat the steel shaft, but that will be somewhat temporary. Plated shaft with a rust resistant surface is sometimes available, but I don't recall McMaster having it.