I have found one of the most concise histories of Dell comics written in Don Markstein’s Toonopedia
I believe the most in depth history of Dell comics can be found as Chapter 6 of Crawford’s Encyclopedia of Comic Books. Some highlights from this chapter include the following excerpts.
A complete listing of the titles published by Dell is provided here as spreadsheet. This spreadsheet includes the number of titles published each year from 1929 through 1973.