I just bought a GMS 40 size motor for my Cessna 182 from Great Planes. The propeller chart for the GMS 40 states I should use a 11x5 prop. I don't have that size and want to fly it this weekend. I do have sizes 11x7-1/2 , 10x8, 11x8, 10x7. The question is, can I get away with one of these. Thanks.

11x5 is a little large for the majority of 40 engines. I would suggest a 10x6 or 10x7 prop. If it is a 46 engine, then use 11x5, 11x6 or 11x7 props.