It's fine to do the swim and bike distances. For my HIM training plans, I have actually ridden up to 65-70 miles.
Look at it this way... 56 miles needs to be EASY. Just a typical weekend ride-ya know? You shouldn't see the distance as "That is so far!"
You can train- even overtrain the distances for the bike and swim and come out fine... but with running it's easy to get injured. So if you only do a couple of runs up to 8-10 miles you will be fine.
I personally don't do long bricks. I didn't do it for IM training nor for my HIM training and I think it's fine. My coaches for 2007 and 2008 thought so to- that's how they wrote my plans.
Short bricks are beneficial I think, and I do one a week. I go ride a very steep hills for an hour (up and down!) and then I run 3 miles right afterwards.
Good luck! YOU CAN DO IT!!!!
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"