Hi Jesse- welcome to the forum- Stop by the intro page and say howdy.
My cross references do not show a Model 40. That may not mean a lot- there were a LOT of companies that made guns marked with the Sears JC Higgins brand. One that was close to yours is the JC Higiins Model 45- which is a Marlin 336 carbine. That is the second most popular deer rifle in the US.
Pictures would help, along with ALL of the markings on the rifle.
What we have here is... failure- to communicate.