I write about the classic FIAT 124 Spider (1966-1985) and maintain a public library of information on classic FIAT automobiles sold in North America.
Maintaining the Italian Roadster
Originally published in 2015, revised in 2016 and currently available on Amazon.com in softcover and Lulu.com in hardcover.
Note: if shopping on Amazon buy the printed book and I believe they give you the Kindle version. Avoid the old white cover version which appears from time to time, its out of print and resold at a ridiculously high markup by some online resellers.
FIAT 124 Spider Engine Maintenance and Modification
Originally published in 1997 and revised several time since, this could be called a home mechanic's guide to understanding the FIAT twin cam, improving reliability, performing tune ups, and making modest performance increases through stock parts.
This library is of documentation I personally maintain and is generally only for the classic 124 series. The most complete classic FIAT documentation set on the web is in the forum library on mirafiori.com - register (free) to gain access.