Aight, those other posters are out of the there mind to say you can't train in the summer unless you are in a state bordering Canada. And that you need to not have a job. Schedule your runs according to the heat and your working schedule. Get a training group to force you to run after an 8 hr work day.
If you are sticking to 70-80mpw with a 12-13mi long run, quality needs to be your best friend. I am a big fan of milage in the summer, but pick what works for you.
I'll give you a kind of fool proof plan to build your aerobic system and strength throughout the summer.
Milage: Build to 75-80mpw by end of July. Depending on your history of running, it is safe to increase milage each week by 5-6 miles. Use the 4 week cycle of three weeks of raising milage, and then 1 week at 10-15mpw down to absorb and recover from the increased training load. Start the cycle again close to your highest week of the summer.
Workouts: I would say a safe bet is 2 workouts a week. I don't really want to name specific workouts, but involve hills, trails, grass, distance. Either long and continuous, or reps with short rest. You are going to race on trails and grass? You bet your a$$ you better make a majority of you workouts on them. It is the law of specificity within the law of specificity.
Extras: The lifting, the strides, the drills all make you a smoother, more efficient runner. Keep that up a few days a week. I am assuming since you want to include them that you already have an idea how you are going to incorporate them into your schedule.
Summary: Disappear into the woods for the summer, come back out a lean running machine. Run by effort and don't focus on the watch. You would be surprised how similar a lot of the collegiate xc team's train in the summer, just at different paces and distances (depending on ability). Stay consistent, enjoy it.
NOTE: What I have seen is a lot of runners have GREAT summer training. Fit, strong, fast. But screw up their in season training due to less focus, bad coaching, etc.