All that cardio is going to need to be fed, that's for sure..
Carbs will keep you hungrier than higher fat tendancies, there are plenty of primal carbohydrates for you to indulge in.. Potatoes & fruits may be the ticket.. Snarfing down a banana, side order of potato with dinner.. Think about clean yogurts with added fruits.. (I personally am not a fan of the carbohydrate, but you probably handle them better than I do.. I prefer to cram my body with higher fat calories)
Fatty meats are fine as well, but I wouldn't spend a lot of room in your stomach on veggies.. You need calorie dense foods or the weight will just keep falling off (I'm similar to you without all the cardio.. eating as an athlete to keep weight/energy/calories up.. not looking to keep dropping weight).. Nuts, fatty meats, potatoes, fruits, whole eggs, yogurt, maybe even drinking some coconut milk if you can handle dairy? There's like 700 calories in a can of that stuff.. All of these are calorie dense & will keep you from dissolving into thin air..
Don't be afraid of what this eating style will do to your body, you're new & the body may be adjusting to its new found nourishment.. A grainless, low toxin diet is feeding you correctly, so the body is certaintly going to drop weight & deflate inflammation as it cleans up.. I personally noticed that my body dropped weight in the beginning, then I started to put back on healthy, toned, proportioned lean weight (which is what you're looking for) while eating less food.. Almost like nature grabbed me, unraveled all the knots & my body sculpted to what its supposed to look & feel like.. It did take a little time to undo the damage from years of eating breads & grains ("health guru" propoganda)
You also mentioned this cardio-craze will only last another 6 weeks, so whatever you do to jam in more calories is only temporary until you can calm down after the race & get back to a normal activity level..