I thought it was strange, too. I know Bottesini is associated mostly with his Testore... (I actually think he had two.)
But, the people I talked to beforehand were positive it was once owned by Bottesini. And I refuse to believe that some fellow bass players would mistake Dragonetti for Bottesini. Plus, isn't Dragonetti's da Salo still i that monastery? Or, maybe he had several? I know the monastery bass was restored in 2007 - it's the one on your photo, right? - but I believe it was returned to the monastery after the restoration. Stupid as I am, I forgot to ask Mr. Styffe about this particular bass' history. It is dated to 1575, though. And it really is a Gasparo da Salo, and is the bass currently insured to the greatest amount of money.
Thomas Martin's online Bottesini biography mentions that Bottesini showed great interest in the makings of da Salo... maybe this one had been in Bottesini's possession during a brief period, too.
No guts! It is used for solo playing these days... and Styffe is known for having a knack for modern stuff... so, definitely no guts.
And, four strings, converted or original I don't know.