yes it's "just" 55 - an assembly manual is exactly what the name says, the "assembly specifications" for each new series from the engineering/design dept, intended for the reference and training of the assembly line crews - an internal document, later reproduced by vendors to help themselves to some of your money .... the next assembly manual prepared by GM was for 1960, and there were
scads of documents specifically for dealers and shops and the public - also note some pages of the 55-59 manual are dated 1954 and earlier
after the first year of a series there were documents circulated internally called 'running changes' that documented the yearly design and engineering updates - find a package of those for each of the TF years and have them reproduced - otherwise the shop manual covers details like torques, and you may be aware that the '59 shop manual is a
supplement to the '58 manual, which itself is simply an update from the '57 shop manual for the minor body changes from the 55-57 manuals
the reason the 'copyright' on the book is Golden State, is that the founder of that parts vendor, Seth Doulton, was very focused on the TF trucks and made an effort to collect a lot of the info available to you today, as well as the engineering specs for many parts that he reproduced or contracted reproduction of, and tons of NOS parts from dealers that were a large portion of his business in the 70's and 80's
Bill