Cannonmn,
Another interesting model (I've never read anything about this cannon before) you've posted on the board; I've got the feeling you could post a picture of a different ordnance model every day, and take up a good portion of the calendar in the process.
In one of the sites you posted it is said that the cannon was made by a Venetian gun founder in 1542; if true, I'd find this history fascinating in its own right, because the Venetians weren't too fond of Muslims at this time, but I guess then like now, gold trumps many other considerations.
I enlarged the pics of the real cannon, and you can clearly see the lugs/projections near the breech on the barrel; the eyes that held the rings on the chase are also clearly visible (I wonder why they removed the rings). I took a good look at the model carriage, and those lugs make a lot of sense; they would stop the barrel from sliding/rotating from the recoil. The early European and English trunnionless cannons were mounted in carriages that had cut-outs, or carved hollows that the barrels nestled in, with their breeches abutting solid wood.