Thanks for the reply, Don! Well, that italian web site you mentioned has simply quoted from the Ezio Pirazzini's book "Storia dei motomodiali - I giorni del coraggio", pag. 26 where it is written that "Nel 1926 le Case italiane organizzarono la prima spedizione in grande stile: ....la Guzzi con le 250 e 350 guidate da Prini e da Pietro Ghersi...". Can you confirm that the Guzzi had a 350cc. machine already in 1926?

Ugo Prini was in the Guzzi team since 1925. Incidentally, the Guzzi team in 1925 included the legendary Guido Mentasti, who won the first European Championship at Monza in september 1924 on a Guzzi 500cc. If he were not be killed 28 years old in 1925 during a race at Brescia, I'm sure his name would have been in the isle of Man TT history!