I don't know about that old of a version of zen-cart. I only have experience from 1.3.8, and up. In all of those versions, placing the customer into a group does not change their order history, and when they log in, there is full order history. When I log in on mine, I get quick reorder through the order_history sidebox. I don't know if the quick reorder is specific to my template, or not.