Actually, the website list two propellers for the O-320. A three blade 68" diameter and three blade 72" diameter. Not easy to find on their website using their standard product search options. I like the simplicity of how the electric prop control works. Haven't ever seen one or read of one installed on an RV but would be curious about the performance also.
I contacted AirMaster back in Dec 2019 and was told the following:
"We have in development the AP725, expected to be released second half 2020, which is expected to be a match for the engines you are considering. Available prop diameter can be 72-82 inches depending on blade choice. Blades from either Sensenich or Whirlwind can be used. "
"Cost is expected to be USD12920 for a complete system, plus shipping at around USD400-"
"Expected weight and specifications for this system, is shown on the back of the attached brochure."
The brochure is here, I couldn't figure out how to upload a .pdf, so it is a .jpeg.