Only way to figure it out is to get it hooked up up as per normal (control head and everything), power it on, and go through the menu to the Features area and read off the feature numbers. There's nothing on the outside of the radio itself which will give you the features.
Because the features in these radios can only be activated via a key received from Harris, they keep a record of that, but you have to go through them to get the information. They'll have a record of what was in it when shipped, and what's been added since then.
Unless you read off the features from the control head, or go through Harris, you're pretty much out of luck.