The SaveGame system already solves this problem. Can you use that? You can set the “not part of savegame” flag on properties.
Another option is to save the name of the property, rather than a number. This will be more robust, and additionally will work well if you decide to send these data as JSON or XML for some reason (like, web services or what not.)
A third option is to make a Map of the names of properties to save and their “ID” for each class, and look up each property in this map. Set up this map in the “class defaults” and then don’t edit it on object instances (make it not instance editable) and all instances of the same class will use the same map.
Define an interface ISaveable that returns this map for each kind of object you want to be able to save.