If I had to chose one chuck for the RT it would be a 4 jaw. That way you can dial in any part perfect or hold odd shapes. I have a 5" diameter Gator chuck mostly for this purpose although I can use on my lathe, I got D1-4 apater plate same time. But it required me to machine a back plate adapter to marry them. So the stack-up starts to approach maybe 5" or more from top of jaw to RT surface. The wedding cake syndrome if you have limited head room. A 3J scroll chuck is quicker but if you get one that is too cheap it may or may not be repeatable, depending on accuracy you're after.
Another option is this ER collet plate. Lower profile but only holds circular parts to limit of collet capacity. You can get them relatively inexpensively. I've seen them with 4 holes too but shouldnt be an issue to drill your own. I think I would also mill 2 parallel flats on the edge so you can grip it in a mill vise & now have a nice repeatable way to grip round things vertically without vee blocks & such.