The newer Holgas have a working aperture selection switch -- cloudy is f16 and sunny is f22 (rounding up to the nearest whole stop). The older ones are fixed at around f16. The shutter is pretty consistent between models -- around 1/100. So "Sunny 16" with 400 speed film suggests that shooting at f22 in bright sunlight will overexpose the film by one stop. f16, by two stops. As such, I think it would be okay to develop normally. If you shot in any other light, you might ask the lab to push it by one stop. But given the parameters here, that might be splitting hairs.