Here is a pic of all that I have...... along with a CRUDE chart of dimensions....
All lengths are with respect to the UNDERSIDE flat area of the head. Head thickness is not noted in references by stud providers.......
It appears like #958 is the switch to the later studs......
Another note in the parts book..... Cars 502-512 used the Italian "bolt" style wheel nuts as found on many other Alfa Romeos, Fiats, and Maseratis.....
Cheers!
Steve