Sorry, I thought is was the one using just yolks that had failed. I think the reason they say 350g oil rather than 200g is because you are using the white as well as the yolk which will take more oil and help the mayonnaise to have a firmer consistency. I haven't tried this particular recipe though, so cannot really comment. I did hear a story of a chef who could make a kitchen sinkful of mayo with just one yolk
As DD said, the MC must be kept in place, or the oil will flow too quickly into the bowl. Let us know how you get on with it.
Hope you get your farm work done. Not sure where you are, but nice and sunny here for a change
JB