Why not a 6" barrel, Walt? I find it balances better than the 4" model.
I've used a S&W 686 for over a decade now. It's a good piece. I'm not a fan of the Hogue "alien sex toy" grips on them and wouldn't recommend them to someone with larger hands. I like Craig Spiegel "boot" grips myself; they're beefy and don't attempt to massage your prostate.
This nice part about revolvers (double or even single action) in your father's case is that you do most of the manipulations with the strong hand. Shooting and loading/unloading are both done with the dominant hand. The nondominant hand cradles the cylinder through the frame to prevent the cylinder yoke from swinging and to keep the chambers fixed while inserting rounds. I usually stuff two rounds, rotate the next two chambers up with my thumb, etc. Speedloaders are better.
Probably unnecessary, but here's an example of how to properly load a revolver:
= LINK =
Making sure the ammunition he uses for self-defense purposes (and thus low light shooting) is of a low flash formula is critical as revolvers can be real flamethrowers with some loads. You'll light up the whole room and blind yourself if you use that kind of ammo.