1. For the Lombard kingdom, you can find a free online version of each of the following:
Paul the Deacon, Historia Langobardorum
Thomas Hodgkin, Italy and Her Invaders, Vol. 6
but I'll be surprised if there's much (if anything) specific to the duchy of Tuscany.
2. In the attached Wikipedia article, there's a statement that Pepin the Short transferred some territory from the Duchy of Tuscia to the pope in 754.
http://en.wikipedia.org/wiki/March_of_Tuscany