Thanks for all the guidance, everybody.
One compllicating factor is that this bird is a finicky eater. For some reason, he won't eat anything much larger than a sunflower kernel or kernel of corn. Field peas, vegetables cut too large, whole sunflower seeds, he just leaves. He'll gobble up millet, finely chopped veggies, etc., but usually won't even go after dried meal worms. He won't touch pellets that approach the size of peas. When we find something he likes, he's excited at first and clucks away, as though trying to call hens to eat, before diving in himself. But after a week or two, he gets tired of that particular item and ignores it from that point on.
As I may have mentioned before, he's an abused bird that we "rescued", possibly from cockfighters who threw him in the street after he was injured. The vets fixed him up for the most part, but he still has injuries that prevent him from folding his wing normally. So maybe he has some sort of psychological damage, or larger pieces of food that most chickens can handle are hard for him to swallow. Who knows? The bottom line is that we sometimes have to jump through hoops to find things he likes. Yes, he's pampered, but he's very good-natured and a wonderful pet. We'd like to keep him as healthy as possible.
Cracked corn and various types of nuts -- cashews, sunflower kernels, pine nuts, etc. -- are a big part of his diet, so long as they're broken up small enough for him. And once in a great while, he does eat some dried larvae. So maybe his diet needs just a fine-tuning, not a complete overhaul. Regardless, this thread has been really helpful (ESPECIALLY GC-RAPTOR's lengthy response) in helping us get a handle on how to keep this guy healthy. Thanks again.