Cross country + weight lifting routine

I was wondering how many of you lifters run distance?? The problem i am having is that i have a medium build on me. i'm 5'6, 150 lb, good deal of fat but i'm strong for my age/weight. I also run cross country. Just this year i realized i cannot be a great cross country runner (running 5k/3.1 miles in 15 minutes or something) as long as i'm gonna be big. I decided to stay at a certain speed and work to be no slower, no faster (so my body doesnt shed muscle!).
running goal: keep my 5k/3.1 mi under 20 minutes and my mile under 6 minutes.
lifting goal: infinitely get stronger! and not be bigger than 180 (for my height)

actual question: Do any of you run distance and lift? If so, do you have these problems too? If so, what do you do to solve them?

you can be big and be a great distance runner. it doesn't happen very often, but check out ben true. he runs for dartmouth now.