Dryflyguy:
I don't know what goes on in a set of Regal vice jaws but the Xuron vise has a simple long jaw with a gap between the halves and a stop hole to keep the jaws apart and "springy."
There is a short screw through the gap that you tighten to close the jaws with a long threaded lever that you can place in four different positions in the screw head to keep it out of the way and facilitate faster hook placement.
Here is a photo of the top of the jaws:
View attachment 1641231787
And you are right about the Vince Marinaro photo, there is a picture of him at his fly tying desk with a Xuron/Phelps/Anglers Roost/Thomas vise on the back cover of later editions of "A Modern Dry Fly Code."
My first fly tying vise was a vise peddled by Orvis that for some reason I think was called the "Orvis Supreme." It was basically fancy a clamp version Thompson A style with jaws that freely rotated 360 degrees and a red plastic coated cam lever.
It also had this little sliding stop lever on the vise head that you used to keep the jaws from rotating. The lever engaged in two positions, one with the hook shank in the "normal" position and a second stop where the hook was slightly canted (maybe 15 degrees) toward the tier.
It was a nice little vise but I was lured into buying a Xuron years later and used it for decades until I sprung for a Renzetti.
FWIW - "True Rotary" is really nice for certain tasks but the only time I use it is when I'm winding conventional hackle, winding floss or ribbing. If I am dubbing, I just wrap with my bobbin.
Bottom line, If I'm not tying a fly with hackle, floss or ribbing, I don't bother and it's a totally unnecessary for just looking at the other side of a fly.
Good move on the Regal, everyone I know who has one loves it and I've been temped myself.