I believe our go to guy is Austen who's a moderator on this site. He has done some great restorations with Jacobsen Reel Mowers and, might be able to provide some help with locating the information you need.
Regarding manuals, I would contact Jacobsen directly as they have been happy to provide what information and literature that they have in past to people who have enquried about it, Jacobsen - Renowned for Turf Maintenance Solutions. I would give them the model and serial number and see what they have. If they don't have any manuals, I will do some research and see where else they could be found online. My friend has contacted them a few different times in the past asking about manuals and they even had some dating back to the 40's and 50's, so I would think there should be a pretty good chance of them having the manuals for your machine.