There is an interesting as seemingly very complete history of the Universal Engine Company at the following URL: http://www3.telus.net/Atomic_4_Eng_Service/History_of_the_Universal_Motor_Company_1.html

It does not mention a Unity Four and I suspect you actually have a Utility Four (25 HP) or possibly a Unimite Four (65 hp). The popularity of the Atomic Four apparently affected the sales of the earlier and slightly less powerful Utility Four and the Utility Four was dropped. The history has pictures of many models so you may be able to confirm this from the photos.