Sorry I can't make it, I have dove the bridge often in the last 2 months.... I am headed north to St. Augustine for the weekend. When you get into the park, the best place to park your car is on the south side of the island, near the playground (essentially in the shadow of the bridge). As Wade's page indicates, if you are doing the west expanse of the bridge, you'll enter the beach to the west of the playground. I like to swim over to the fishing pier first and head west under it. About half way down the fishing pier there is a pile of old pilings that house many tropicals, an occasional eel, arrow crabs, shrimp, scorpion fish, young lobsters etc. etc.. You can spend 30 mintues simply hovering over this spot watching the sea life, but watch for fishing lines/hooks and bring shears or a knife to cut the line if you get hooked. At the end of the fishing pier, I either turn south and head to the main bridge, exploring the open space between the structures (I've seen many batfish and flying gurnards in this area) or I CAREFULLY continue west until I get to the barrier wall that separates the boat channel from the diveable area (if you are going to head west from the pier towards the barrier, its not a bad idea to surface at the end of the pier and get a visual on the barrier so you know how far to swim.... if you accidentally start in a northwest direction from the end of the pier, you can accidentally wander into the boat channel... not good). If I head west from the pier, I then head south along the boat channel barrier until I get to the main bridge. Once you hit the pilings for the main bridge, you can explore the pilings around them as you head back east. The main bridge piling that is closest to the barrier wall is really intersting if vis is good. It is almost wall-like with many critters.
I have done one dive on the routes noted above which lasted about 1 hour 40 minutes. If you have extra time, you can swim south from the beach area and find a couple of sunken sail boats (the top of one is visible from the beach) which house tropicals. sometimes you'll find rays, barracuda, batfish, sea robins, in the open sand area. Be careful not to head into the south boat channel and don't let you dive flag drag along any boats that are moored in the area... the owners get honked.
you can surface any time to get a visual just to make sure you have not wandered where you should not be.
sorry I can't join you.... you might want to send a PM to westpalmdiver.... he is familiar with the bridge too. he and I plan to dive the bridge after work on thursday