I aggree, that where & how the steady will be used is an important question, because they're actually 2 different setups in most cases. The size of the bearing you use may also be relivent to how it will be used.
If It's needed in between centers on the lathe, then probably have an easier time with a flat bed lathe that's slotted like some better wood lathes are, because the mount may be easier to fabricate, but alignment may become a issue unless you can overhang the steady on one side of the bed to help keep it aligned. That may be solved with a longer bearing or steady also, because it will somewhat self align it'self when you slide the work piece through It, but I don't know where to get those, and probably expensive if they were located.
Obviously the easiest to fabricate might be with the use of a flange bearing, and strong angle bracket for the mount. With that setup I would drill/bore for, and mount the bearing last, so I can align and center it with the lathe easier.
btw You could also mill the bottom of the mount to fit the slot in the bed, or attatch a piece of stock that is the width of the slot to the bottom of the mount. That is providing that the slot channel in the bedway runs true. you may also be able to use a self aligning bearing setup. the list goes on and on on how to do it, just have to figure out the best suited method for each paticular setup.
If you want to save yourself the aggravation, then I would call Chris & ask him first also. He already has some lathes figured out & setup to fabricate the parts, and for what goes into making them, he is reasonable on price. I've got parts for stuff I was making from him that I could have made, but when I figured out the cost to buy the parts to do it myself, I found It was well worth the little extra to save the time and aggravation, and put It toward something else I needed to build.
If you need more of a specialized mount, A machine shop may also be able to make you a base for your mount, and might even be familiar with or able to find the specs on your lathe to make explaining what you need easier. I have had that done also with mounts by someone I knew, and traded some production cues out for the work. He thought I gave him way too much for the work, so might not be too expensive to have done depending on the mount type needed.
Greg