If I'm not mistaken, since you have fixed sights, you should need a front sight with a .055 narrow tang.
Here is what you need:
http://www.amazon.com/Trijicon-Nigh...W0/ref=sr_1_11?ie=UTF8&qid=1327005169&sr=8-11
Are the sights on these RIA's staked or fixed? If those sights would do the trick, that's an awesome find!