I made a very basic securing plate from a piece of hard maple......
and settled on this means of attaching the wheels to their arms......
With the result that the rest is finished and awaiting a turning project.....
Only after use, will I know if this design is good/bad.....but I can say now that this method of attachment to the lathe is very secure.....the rest seems very stable.....so, I think it will work well for me.
I made a very similar one, using a design by Dom, when he still hung out here. I used the same wheels as you have, and while they work very well, I need to find some substantially smaller ones for really small spindles.
To check the minimal size of diameter these wheels would allow, I used some drill bits and a caliper and found that with the three wheels touching a minimal diameter was 39/60" or just under 5/8".......
So, if you turn smaller than that, you'll want a smaller wheel.