Carl an 11/7 is to much load for those GP magnum forties. You will run the risk of constant overheating and the resulting deadsticks.
All is not lost as Hoss suggested you certainly can cut it down and I would not get fancy about it and just use a straght cut. Here in the first photos is the best procedure for cutting down a prop to assure both blades have the same length. For that small venturi engine I woud cut it down to a 9.5 /7 and do not try to change the blade planform or pitch. Of course do balance agine after cutting or reshaping.
The last photo is a typical modelers supply of props. Nope ya never can have enough.
John