To me the single biggest advantage that low carbing has is the appetite drops after a while. The body releases insulin in direct response to dietary carbs so low carb means low insulin means no carb cravings.

It's nice not to feel hungry for 6 to 9 hours.

tricks to avoid constipation?

First question I have is about empty versus plugged ...

I ate some well-cooked rib bones. I guess the extra calcium was
plugged up the works.

Fairly few folks take the route of lowering protein in favor of fat. It works well but it's far more common to lower fat in favor of protein. You are now seeing the advantages of making that less popular choice...
I suggest that the food you're eating now is likely to get dull from the
extra fat. Care needs to be taken to keep the food from seeming
greasy.

I saw one study that concluded the minimum protein requirement is
between 0.4 and 1 g/kg. I am hoping to add more protein later, once
some inflammatory symptoms subside.

The body burns carbs entirely for fuel ...

Thanks for the detailed explanation of carb, fat and protein
metabolism.

But you're at 50 grams of carb. As you are you have the option of going down to 20 grams of carb in exchange for some more protein ending up with leaner cuts that are easier to find. A cycle of alternating weeks at 50 and 20 grams of carb, protein grams to match the same total calories, the same fat grams - That would be a cycle that rocks for how it effects the hormone released in response to diet.

I'll try exhanging the legumes for some meat and see how it feels.

I do a short, medium-intensity workout infrequently. It seems I get a
mild headache later in the day and into the next morning. Can I add
some carbs before of after the workout to avoid this? Does the body
resort to cortisol if carb reserves are too low? Do you adust your
carbs based on physical activity?