My condolences on your loss.
These were a fairly common catalog option, made and marketed by Ruger to directly compete with the Smith & Wesson model 10 (blue) and model 64 (stainless) .38 Special revolvers, which were still popular with security and some police departments at the time. To change it to a conventional single- or double-action mechanism again, I'm not sure if you'd just need a hammer, or a trigger and a hammer (properly fitted, of course). Hammer replacement is easy; trigger, not so much. As most departments switched-over to autoloading pistols, these guns, like the similar S&W models, were dumped onto the used-gun market in huge numbers. I can remember seeing the Ruger and S&W versions of these guns at gun shows for $100-$150 each, and I even bought a few (kicking myself for not buying more, and keeping them all!).
The DAO mechanism does not enhance the value as most folks do not shoot revolvers in DA mode nowadays, but it probably doesn't matter too much because the caliber by itself will kill it for most purchasers looking for a 4" revolver. It's the same size and weight as the .357 Magnum models, but chambered for the far less powerful .38, and that makes it less desirable for the vast majority of potential buyers. Don't get me wrong, I'm not a hater; it's a fine gun, I've been a Ruger fan for decades, and I've owned several sub-models of that series in my lifetime, all of which worked just fine.
It sounds like you might be considering selling it. If you don't mind some unsolicited advice, I'd offer that unless you REALLY need the money, I'd recommend keeping it and learning to shoot it in DA mode. DA revolver shooting seems to be a dying art in most areas, and good DA shooter gives up nothing in practical accuracy to a SA shooter, and can usually shoot those good shot groups twice as fast (or much, much faster; run a search for some Jerry Miculek revolver shooting video clips).
In closing; it's a fine, solid gun, probably with a lower-than-average resale value due to its configuration and caliber, but still darn useful and super durable.
Also, one of the few revolvers designed to be field-stripped like a semi-auto pistol. The original grip screws had a wider-than-normal screw slot, so you could use a cartridge rim to unscrew and remove the grips, and using a short metal pin stored under the grips, a person could disassemble the revolver as far as needed for a good cleaning or to remove deposits of sand/dirt/mud picked up in the field, which will jam most revolvers in short order.