I incorporate lifting into my running routine as winter nears and I'm getting ready to start ski touring again. Granted, you're asking about training for an actual running race, so we're comparing apples and oranges a bit. However, I used to be an Army Master Fitness Trainer, and I moonlighted for years doing personal training, so I do know a bit about this.
First, why tie yourself to a 7-day schedule? Why not try a two-week schedule or a ten-day schedule? Or something else? I use a ten-day schedule because it's a nice round number and it gives more flexibility. Think outside the box.
You're right to be concerned about over training. It's usually the problem when my clients used to hit plateaus. For people who are addicted to exercise (like most people on this site), it's tough to force yourself to rest. Doing leg exercises followed shortly by running will be overall detrimental rather than helpful because you're not allowing your muscles to grow. Remember: you don't get stronger in the gym. That's where you break down and weaken your muscles. You get stronger by resting them and providing them with proper nutrition.
As far as exercises, I'm a big proponent of free-body exercises (where your body is the resistance) and powerlifting movements. I never use machines. My routine to get ready for ski touring season is centered around a few powerlifting movements. A typical workout would look like:
Six sets cleans
three sets clean-and-jerk
three sets snatches
two sets full squat
two sets straight-leg dead lift
calf raises with bar on back
Then, two full days rest where I eat everything in sight. A few days later, I do a light upper body workout with pull-ups, dips, ab exercises, etc., all free-body or with weight tied to my waist. I incorporate hill running throughout until day 10, when I start over.
The only other advice I have is don't get stuck in a routine for too long. It's boring, and your body will get into a groove. You need to constantly change things up to hit different areas.
Big caveat: If you've never done these sorts of powerlifting movements, it's very easy to hurt yourself, especially your back. Make sure someone helps you out and watches your form to ensure you're not muscling it up with your back instead of your legs and ass.