Very interesting. The immediate post-New Deal era was the closest the US ever got to class-based voting. How did you happen to come across this?
Several years ago I was lurking on AlternateHistory.com and someone posted one of those Field polls in PDF form, and I checked out the main site. You can't access them directly from the UCData Berkeley website anymore, but someone used the Wayback Machine and archived all California Field polls from 1946-1995. I haven't read all of them, but plenty of good stuff about everything from the Marshall Plan to Prop 187.
For those who are interested in such things:
https://web.archive.org/web/20170805130744/http://ucdata.berkeley.edu/data_record.php?recid=42