Some things you can do:
1) Use a huge rubber bungee cord. Take two eye bolts, mount them to the existing holes, and strap them in with the bungee.
2) Grind some metal away to clear the posts
3) Get yourself an Optima 34/78 top battery cover. Requires modification of your bracket bolts to accomodate the extra thickness.
http://www.batteries.com/productprof...p?appid=320134
-Steve