How does 60 miles break down over seven days? The longest week I've done is 40 miles. That was:
Monday: hill intervals that added up to 3.5 miles including warm up and cool down.
Tuesday: 4.7 mile fast, flat run
Thursday: 10 mile race pace
Saturday: 22 mile race pace (or a little slower)
I look at that and don't know where I'd add an extra 20 miles. Even if I replaced Monday and Tuesday with 10 mile runs it's still only 52 miles.
Do you run twice per day? How many days a week do you run in a week like that?