AttachmentMaker is used for inserting missing attachment points when one gets an error. I haven't used it to manufacture new attachments there were never intended to be there (e.g. attaching cabs or anything else to a model, which is what it sounds like you are trying to do - correct me if I'm wrong) but, then again, I haven't really tried very much. I think there might be a lot more to it than just adding attachment points (for one, I see the asset kind is "interior") and there must be a way for the cab asset to be specified as a child object of the locomotive asset, which is something AttachmentMaker won't do.