How do these divine offices differ? Is it like the difference between 1962 missal and 1955?
It's mostly a lot of deletions.
The only thing that was really added rather than deleted when you compare 1950 to 1962/3 is the Feast of St. Joseph the Worker. The creation of that feast and it's placement on May 1st necessitated the Feast of Sts. Philip and James (previously celebrated on May 1st) being moved to May 11th. May 11th was previously a feria, so the Office of May 11th is the only Office I'm aware of in the whole liturgical year where the amount of reading for the day would've increased
when comparing 1950 to 1962/3. As a feria it would've had Matins of 3 lessons and nine psalms along with ferial psalms at all the hours, whereas May 11th becoming a feast of the Apostles made the day have 9 lessons and 9 psalms at Matins.
Aside from this addition (along with additions of other Saints' days that would've been approximately the same length as whatever they replaced) here are some of the notable changes/deletions:
1) Feast rankings (1950: Double 1st Class, Double 2nd Class, Double Major, Double Minor, Semidouble, Simple, Feria; 1962: 1st Class, 2nd Class, 3rd Class, Feria)
2) All octaves were abolished except those of Christmas, Easter, and Pentecost
3) The recitation of the Our Father and Hail Mary (as well as the Creed before Matins and Prime) before the hours was abolished.
4) The change of the doxology (last verse) of hymns was mostly
(not entirely) abolished
5) 1950: Double 2nd Class Feasts use festal psalms; 1962: 2nd Class feasts use ferial psalms at most hours (with exceptions).
6) 1950: All Doubles 2nd Class take precedence when occurring on most Sundays; 1962: all Sundays take precedence over an occurring 2nd class feast.
There are many other differences, some big and some small. Also, some of these changes were actually made in 1955, not 1962.