All the pouches on the vest from the armyissue link are fixed, you can't replace them with holster on either side, but you can use a pouch like a holster as Cheese said. If you want something modular, go MOLLE. Believe me, I started off with a similar vest, but ended up with MOLLE anyways. People like to customize stuff.
http://stores.ebay.com/eHobby-Asia-A...2QQlnsZ1QQtZkm