I saved one from a scrapper and its being rebuilt by another fellow in our club, I did some research on the trucks when I was buying mine and according the the OPP manual they were expected to get around .75 MPG I am expecting that to be with the 844 ci gas engine and not the Cummins 300. The trucks with duals are to wide to be driven without permits in ND! Parts are going to be your biggest challenge, a friend of mine in SD did a major rebuild on a 123 and he thinks he got one of the last Cummins 300 diesels in the US and lot of the transmission and transfer case pieces had to be ordered directly from Fiat in Italy, since they own MACK. Its hard the Italy does not like the US and it seems they take a very personal pride in making things difficult for us. The trucks are truly works of art in my book and I love BIG trucks. But with all that said the truck you found could be given to you for free and your going to have more into it than buying an already completed restored 123 and its ready to go. Its always the guys spending the money on the restoration that loses his butt!
Karl