50 miles?? Kudos and big respect for that, that is a seriously impressive achievement. Most Marathons never go beyond 25-26 miles.
Like Sarah said, if you do the sort of things she mentions, you will work with some of them, multiple muscles at the same time.
A good one would be Bent over Barbell Rows, for things like Lats, Rhomboids, Traps to some degree, and a bit of Arm work goes in there for good measure. That way if you do exercises like Squats for example, that hit multiple muscles, you cut down on workout time, if 20-30 minutes is an ideal limit.
You would probably be best to start off light on the weights, get used to them, and about 4-6 weeks in, go for a more challenging level. You'll need to give your muscles time to adapt, so you don't want to go full body workouts, and then cane the weights.
You will then be able to get used to Loadbearing and correct form / technique. Be patient, and it should come together nicely
Normally many people would say do Cardio after weights, as Cardio could deplete energy levels, and possibly affect weights, but in your case, with your Marathon style training, it might be best to do it before weights, so you don't fatigue your Muscles with weights, and then jeopardise their recovery, by running, or indeed affect your running.
That would mostly apply to the Legs really.
It's not likely you'd ever need to get to the point, where you were doing full body workouts, with a heavy 6-8 rep intesity, or failure style training, so Cardio effects on weights, (even after some time of adjustment, and increased weight levels), would be more than likely small, and I don't think you'd be training weights hard enough to have Cardio affect them.