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 - 3rd edition!
Originally published in 2015 the new 3rd edition was released in December of 2018. It is available in color and black and white, softcover, from Amazon worldwide:
Black and White Printing (Softcover)
Note: If you buy the print version Amazon will give you a Kindle version. I don't recommend the Kindle version unless it is free - the book has yet to be optimized for the format.
FIAT 124 Spider Engine Maintenance and Modification
Originally published in 1997 and revised several times 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.
Documentation libraries
The most complete classic FIAT documentation set on the web is in the forum library on mirafiori.com - register (free) to gain access.