Hi Denis,
Can't be a lot of help as I can only use the same source as yourself, Namely "La Lancia, so anything between the build figures and years would appear to be an educated guess, going on the facts you have.
I shouldn't think the dates on the cylinder head & block would really have a lot of bearing, having been in Motor Manufacturing for 25 years before moving on, that is either the first date of the castings or the year that particular component was manufactured, but unless there were changes to the component, the stock of old would be used up first, so theoretically the whole run of cars could have had the same date on them.
However if this was different as far as Lancia were concerned, someone with a greater, more specific knowledge than myself will hopefully enlighten us.
Regarding the chassis Number Commencing at 1001, that is correct giving a total of 3052 built 1959-1962.
Regards
Brian Hilton
8227