I want to put on some muscle and get a little stronger and faster for the 800m ,mile and 400m in track?

Ok so im a senior i ran 16:31 5k in cross country this year and the season just ended. Now its the off season and i want to put on some fast twitch muscle and get stronger for my 2 events in track(800 and mile) to help me with my finishing kick, which i have lacked for the past three years in xc and track. The only problem is that during the off season i run with and lift with the cross country team, and we do a bunch of 8,9,10 mile Long runs and medium runs during the winter,which is good for endurance, but not necessarily for speed and power/strength and i end up going on these runs after we lift. Which to me defeats the purpose of lifting, because its over training. For example well lift with low weight and high reps a bunch of times and then go for a long run or medium run after AT A GOOD PACE.!! THE bottom line is how do i go about gaining some fast twitch muscle during the off season while maintaining my endurance,im 5,8 about 140(lighter during xc and track) pounds of slow twitch and would like put on a few pounds or at least get some fast twitch muscle(power,speed). And what i said earlier about working out with the team its not mandatory, we sort of do our own thing. which means that i dint haft to work out with them i could come up with my own routine, i work out with them to make sure that i am were im supposed to be on the team,one of the faster runners. Also if i could i would like to move up to the 400m dash. i ran a 2:02 in the 800 last year and 55 in the 400m.