The year was written in the manual. Given the fuel port clearly states gasoline, have to conclude the manual was not original. Thanks for all the feedback. Pretty sure there will be more questions as I dive into possible ownership.
The Bobcat 543B (1992) manual (original with unit) and all info on web says diesel. Fuel label says gasoline. Kabota engine. 2700 hours. I will look for engine serial number next, hoping for clarity. Any other ideas or useful information?