Interestingly, I found a pdf that introduces Clascal, which later was renamed Object Pascal. Clascal being a play on words of Pascal, as in Pascal with Classes. This talks about the concept of Clascal, what inspired it, and differences between it and versions of Pascal at that time. Also included is a download of the Lisa Pascal manual, as it's referenced in the Clascal document and the extensions were built on top of it.
Download PDF- An Introduction To ClascalDownload PDF- Lisa Pascal Reference ManualAnother thing that tends not to be discussed is that Wirth acted as a (AIUI paid) consultant to the Ada design process. It's interesting that later on he appeared to be very hostile to OO, arguing that everything could be done adequately using records.
Yes, information about Pascal's and Wirth's connection to Ada is hard to come by too, though in looking at Ada, it becomes readily apparent. Even Wiki makes no mention of Wirth's influence on Ada, though gives a brief mention of Pascal.
As for OOP, there is a famous quote attributed to Wirth, "Nevertheless, I consider OOP as an aspect of programming in the large; that is, as an aspect that logically follows programming in the small and requires sound knowledge of procedural programming."
I can see where Wirth is coming from, because Pascal has records, nested functions, variants, and units. OOP is very much a choice, as oppose to a necessity or forced paradigm like it is in various other languages. From that perspective, OOP is used when appropriate or where it makes sense versus "if all you have is a hammer, everything looks like a nail". Wirth may have seen through the hype early, and knew OOP was not necessarily the "be all, end all". There is composition versus inheritance, modularization in contrast to OOP's take on encapsulation, and polymorphism is not owned by only OOP.
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