The window well should extend about 12" below the BOTTOM of the window / ledge. Fill with 3/4" gravel to just below the drain. Excess water should be allowed to rise up to the drain and then fall into it.
I don't know where you can find any info. However, go to the Home Center or Lumber Yard and look at the mfgr. labels on the wells. Write down the info. If there isn't any info, go to the Building Materials Desk or Customer Service Desk and ask them for the info. Write down the SKU info on the UPC sticker. Then, you can contact the mfgr. for, perhaps, some instructions.
As far as being a big job, I did one in the summer of '99. The ledge was only about 18" below ground. The TOP of the well wall should be about 6" above grade. It wasn't hard - Just time. Since I don't have a drain, I had to dig mine deep enough so that whatever water ran into it would be absorbed BELOW the foundation. (My pit was about 3' deep. I just filled it w/a lot of gravel.) Anyways, you're not done until you grade up to the top of the well-wall so that whatever water runs up to it will NOT run over it. This is the key - To keep water OUT of the well. So go a little higher and grade around it so it has some slope around it. Then, DON'T buy those cheap plastic covers from the Home Centers to cover it. Go to a Lumber Yard and ask for the HARD plastic well covers. You don't need to attach the well wall to the foundation. Just have it sit on the gravel (so dig out a little wider than the half-moon so it can sit on the gravel.) Tamp 2-3" of dirt around the perimeter (on a slope) at a time. DON'T try to tamp it all at once. If you don't tamp, you'll have 'settling' problems.
I can't find any help on the WEB for this project. Use your existing wells as a 'guide'. Or try to ctc the mfgrs that are listed on the wells. My best to ya and hope this helps.
Jay J -Moderator
PS: The wells come in different heights. YOu're gonna have to do some measuring around the window you're working on. Bring that info w/you to the store(s).