There is "The Atlas Thread" that has all the answers but in a nutshell you owe them 17 days a month, a bit more than 2 on/2 off. Sixty day lines bridge the end/beginning of the month. You owe them 34 days over the two months. Think 10/15/9 with 7 days of the middle block in the first month and 8 in the second. But I've seen 4/17/12 and 12/5/14.
All the bases are 747 bases. Only CVG and JFK are also 767 bases.