I'd probably trust one of the spoke calculators that I've used. I like this one but I always try a number of them to compare results (which are typically all close to each other). My skeptical nature would not completely trust any builder though, but knowing that it's Peter White adds a lot of confidence. I hope he can come through for you.

In my volunteer work rehabbing donated bikes for charity organizations, I encounter a lot of broken spokes. I find it more expedient to remove another good spoke and measure it since it would take way more time to determine the parameters to then plug into a calculator.

Have fun on your tour.