Looks like Flite Test recommends a 10x4.5 2-blade prop for the C-Pack.
Doing some math to figure out the prop loading, a 4-blade prop that has a similar prop load and pitch-speed to the recommended prop would be something in the 8" to 8.5" diameter range.
All that said, 4-blade props are pretty hard to find, especially ones for planes of this size.
The nearest size I could find is a
7x5.4 4-blade for an FMS P-51 mustang. I have no way of knowing if this prop would fit your motor or perform well on your plane, but it's somewhere to start anyway.
Edit to add: a 9x4.5 3-blade should be a pretty good fit if you can't find a 4-blade that works.