Some manuals and parts lists for vintage Jacobsen products are available in the company's archives. You must provide the model and serial numbers of the piece of equipment you are seeking information for. Their customer service can be reached through "contact us" at the top of their page.
I was just poking around on the Jacobsen/Textron site and found something that I had never seen before. It's a drop down menu for Out of Production models, and among them are the vintage Lawn Queen, Lawn Prince and Lawn King!