According to Massimo Clarke in “La Storia del bicilindrico Mondial 250” [Motosprint; dec. 1990] Mondial developped three different desmo-systems. The first one was like the Delage-system. The two other systems used two two-armed rockers per valve. Unfortunately in this article no more text/pics.
Source italian texts (near pic) : Luraschi, A., Storia della motocicletta: gli ultimi 20 anni, deelS, Milaan. p.263.
According to my Motto: “Never assume anything, observe the obvious”, I added the Mondial to the “Mystery-Page”, because no-one ever saw the interior desmo-parts of the engine, because….. (as we know now) they were never there.
After 45 years Mr. Pochettino – the actual owner of the bike – revealed that the Mondial was NON-Desmo! Source: “Rettifica! (45 Anni dopo) by Carlo Perelli In: Motociclismo d’Epoca” of february 2002.