Andy,
The 24x10 is the correct prop for your 58cc. 26x10 is number two choice. My Evolution 58 started off running backwards a few times when new but after a couple gallons of fuel it no longer has that tendency. Both brands of 58cc use the same ignition. Is your's brand new? Give it a few runs and see if the tendency goes away. BTW, the factory recommended prop for the 45 is also 24x10 and it does turn it very well however users might experiment with 22x8, 22x10, 23x8 to see the maximum output of that engine in 3D applications! RPMs on both of these engines will go over 7000 on the ground depending on exhaust and prop choices. These are two very good engines for enthusiats that like to fly a lot!
J.