Carlo, as Richie and Mike have said, the Ducati 750 Montjuich came originally with a muffler made by Verlicchi.
It has no numbers stamped on it. Please look at the photos.
To register my Montjuich, I had to put on a Conti muffler exactly like yours. I took the Conti off and put the Verlicchi back on because, with the Verlicchi, the music is the best in the world.
Like yours, mine does not want to idle, only wants to gooooooooo......
The last photo shows the Verlicchi stamped "RISERVATO COMPETIZIONE". That is the one on the Montjuich.
The pipe is like the Verlicchi used for bevel twins but it is not the same. See
http://annunci.ebay.it/annunci/ricambi-e-accessori/verona-annunci-bussolengo/trombone-verlicchi-x-ducati-900/38339318The other photos shows a Verlicchi stamped with the English translation......
The two pipes are exactly the same except for the stamping and the black chrome. I bought the "English version" many years ago in Japan (?) for my Laguna Seca and was told it was part of the optional "F1 race kit". I believe anything......
Sorry the photos are bad but I am useless with cameras.
Lastly, um, I humbly point out that we are talking about the Ducati Montjuich, not the nice Laverda 500.
Ciao Amico mio, now it all starts to make sense, I think it will be a hard struggle to find an original pot, though for now I go on like this.
Thank you all for your help, and I can confirm that the Laverda 500 is very nice!
I have done endurance with laverda sfc official Augusto Bretons, and we also did the First Place!