Paul, it's good to hear from you again! I've had this pattern all my adult life. "Into" photography for awhile, then not, then back into. Lather, rinse, repeat.
Anyway, as I understand it, one reason for the fine grain of color developers is dye-clouds. Each little silver-grain is surrounded by a larger cloud of dye, so the grain does not need to be developed as much. That lower development means finer grain. But B&W films don't contain color-couplers, so they will need more development than C-41 to make grains larger, so grain probably won't be as fine. But I encourage you to try it and prove me wrong. I'm not joking! I'm surprised at how often I get surprised by developers.
The matter of the dye clouds is a good catch, Mark. We shall see. I just ordered more Unicolor and will mix the bleach and the fixer as seperate baths.