Training & Nutrition - ride mileage question

I'm trying to line up my training rides for the MS150 from Houston to Austin, but I have a mileage question.
I've already signed up for a 104 mile ride the weekend before the MS. I'm planning on doing the entire route, but will play it by ear as I want to make sure I recover before the MS.
Anyways, there are rides 3 weekends in a row, and I was going to do 40 miles, 70 miles and 70 miles to build up to the 104 mile ride. My longest has been 63, so getting to 70 isn't a problem, I'm just wondering if doing 70 mile rides two weekends in a row is a good idea.
Any advice is much appreciated.

I think NOT doing 70 mile rides two weekends in a row is a bad idea. Not for training purposes, just in general.

That's kind of what I was thinking too since I'm supposed to be building fitness, but I generally like to get other opinions.
Thanks.

How did you feel after doing 63 miles? Were you ready to go the next day? Did you walk funny for a week? You should be able to do the long rides and still feel like want to ride the next day. No reason not to do the mileage on successive weekends if you can handle it. A lot people around here wouldn't bat a lash at doing 70 miles on back-to-back days, let alone weekends.

It depends on your current level of fitness.

Actually, that's the funny thing. Even after my longest ride, I've never been just drained. Now, after the MS150 I'm sure that'll be another story. :)
I looked at a few different training schedules and they all have rides of that length by that point.
Thanks for all of the advice.

As long as you do not red line yourself in the rides, doing 70 mile rides 2 weekends in a row should be no problem. You have a full week to recover. On longer rides, what beats you up is pushing a pace that is too much for you. Generally you are not punished so much if you ride within your capabilities whatever they are.