Can only offer an opinion as I have only trained 3 times a week as per programmed, but something is better than nothing. So my guess would be to do something like workout A on Tuesday and workout B on Friday of each week. Since the weight won't be heavy for several weeks, you should fly through the program as your main focus will be on form. At some point in time, after a few weeks, the weight will start to become heavier, especially on squats and this might affect your marathon training...but maybe at that time, you will have completed the Marathon and it now be a moot issue. When your marathon training is over, then get into the three day a week schedule with the alternating workouts to increase the needed volume and frequency the program calls for.

With all of the running and now added weight training, I would make sure my diet was dialed in. If you have never strength trained or it's been a while and you are getting back into it, you will make what's called newbie gains in strength and muscle. Having calories available to your body will help with growth and mainly recovery (again once the weight starts getting tough). If your goal is weight loss, then keep your calorie deficit to a minimum and protein up. There are plenty of stickies on the other forums that goes through setting macro-nutrient goals for your daily consumption.

And I agree with the previous post, hit your macros and eat a surplus.