Now, that's interesting that a letter I wrote 17 years ago, has turned up. I can say that in all the 17 years the modification has worked well for me. I also can say that it lasted about 40'000 miles and then had to be replaced. Of course, it depends how the second gear is used. Perhaps less in a relatively flat country, but here where I live, sometimes second gear has to be used uphill for some length of time.
The modification may only be successful when the the bearings of main shaft and lay-shaft are in reasonable condition and the gears themselves are not worn too much. And it is to note that the noise will not stop completely as the first and second gears are straight cut.
Lesson learned: rollers or balls running on chromed races doesn't work long, no use!
Cavalitto sells first and second gear sets.
https://www.oldlanciaspares.com/augusta_eng/transmission.phpKarl