Another interesting read is Phil Maffetone. While I don't think he specifically mentions ketosis, his training plan is for athletes, specifically runners, to cultivate and stay in a low-carb fat-burning beast mode for maximum performance. Use of carbs on race day is fine, but you should be capable of maximum aerobic fitness as a fat-burner.
As for the weight gain, it might be necessary to endure a short period of weight gain at first. Either that or put up with both feeling hungry AND low carb flu. I've been trying to keep my calories reasonable while readjusting to low carb once again, but having a heck of a lot of hunger and not being able to keep my calories as low as I "think" I should keep them. I might be wrong about how low they have to be, or it might just be that once I'm fully adjusted it will be a heck of a lot easier to keep my calories in check. I'm thinking it'll be the latter or a combination of the two. In any case, so far after a week of nearly 2000 calories every day, I haven't gained any weight. And today I don't feel super hungry at all. I'm thinking maybe tomorrow for the first time in ages I'll be able to pull off a fast.
My only real issue with the reduced protein thing is that it makes meals kind of boring, small and runny.
Female, 5'3", 50, Starting weight: 163lbs. Current weight: 135 (more or less).
I can squat 187.5lbs, press 75lbs and deadlift 200lbs