Best Prop pitch for an Ericson 32-2 with an Atomic 4 gas?

[BilgeRat]

My son and I have launched our 32-2 and we found that the used propellor we bought from Craigslist was pitched way too little for the vintage 1964 gas Atomic 4 - there are no numbers on it. Can anybody clue us into what might be a better fit?
Thanks in advance for any guidance.
Jay and Ebben