Well, I don't have alot of detailed pics, but I can show what I have.
First thing you do is take out the headlight assembly. Fairly easy, a few connectors and 4 nuts, 2 at the top and 2 at the bottom which are a bit of a pain to get to.
Next, take some masking tape and put it on the metal that is about to be cut. Measure your battery and draw its length and width on the masking tape. Carefully cut the metal and remove. You will notice below that piece of metal is the horn and a bracket that holds up that corner of the fascia.
Here is a picture of the cut hole. Notice I didn't take my advice and draw the battery dimensions so that I have a nice clean hole 

You can take your own measurements and get a battery tray made, or use the dimensions I've already supplied. My tray is big enough to hold a standard size fiero battery, and does not go down so far as to interfear with the fascia. Best to make this out of aluminum so that it does not rust. You can get the metal at any machine shop and have them bend it on a brake press to get the shape and measurements you want.

You can see my measurements sideways were alittle off but it is perfect front to back. Its actually pretty snug, it won't be moving around very much. On the bottom of the tray you can install the stock battery hold down on one side and a lip on the other to keep it rigid.

I have the lips of the battery tray fastened with metal screws, its not going anywhere. Its a close fit with the headlight in place, but there is plenty of room for my cables and posts.

That should be some help, for additional pictures visit this thread. Aaron 88 did a very nice install.
http://www.fierodrivers.com/forum/index.php?topic=765.75