I see that John was also doing some research on your radio for you. I have not been able to find a better source price wise for that repair manual for your radio. I am told that the manual you want is the Howard W. Sams AR-6 book, picture below.
Auto Radio Service Data Manual (A Specialized Volume of PHOTOFACTS Folders, Volume 6, AR-6, This Volume Covers 1955 & 1956 models of auto radios) Amazon wants $45.90 for it plus shipping costs, whatever that would be to Italy.
It is the only source I have found so far. I can tell you this though. The Ford Part # for your Motorola 69MS T&C radio is: FEF-18805-B. I found that information on a website. That IS the correct radio for your '56 Tbird, says Gary Tayman.
Here are a couple more sources for this.
For sale for $7 US.
For $14.99 Not listed as being sold.
Here is the service shop manual for the 69MS, for $29.99.