If you will be using the Spinervals, they recommend an approximate gear combo / resistance, along with (typically) the heart rate you should be aiming for. Heart rate is related to power output (though it lags relative to power)... so you will be getting the right workout for your capabilities at the moment.

Another book you might want to take a look at is Ride Fast, which is aimed at increasing speed, culminating in a personal time trial / race. The book is aimed at cyclists that have gotten bored with riding due to not being able to break the 20 mph barrier. It assumes (I hope!) that the cyclist already has a reasonable base.

If you feel you already have a reasonable base from running, and/or want to try some shorter more intense workplans, the book above or Carmichael might be the plan for you.