My inexpert view is that it is better to run after the workout rather than before. For me simplefit is much more taxing as an upper body workout, so is a good complement to running. Personally, I would recommend just adding simplefit to your running program, I don't really think you would need to change it that much. You might find you are a little slower on Simplefit days (especially day 1) but I wouldn't expect too much of an effect. Unless you are planning to be an everyday runner, you could also alternate simplefit and running days.
Obviously, if your goal is to be an elite level runner, you'll need some coaching with more scientific ideas about weight training programs.