I've always just done .015 inch intake, .020 exhaust - works fine on an identical (aside colour) Wesco. But as Norm said, don't feel you need to be spot on
Also I have found they have a propensity for fuel leaking past the needle whilst sitting between mows (even if the carby is good). Get a cheap inline fuel tap, cut the fuel line and install. Turn off after last mow and turn back on 20 sec before you try to start.
Don't know if you would succeed in getting a customer to do that though
