Yes my claim is about the IDE experience shared across all Xerox PARC environments, and how it affected the design of each language individually.

I will hunt down the papers.

We should not forget that the original Alto operating system(s) had a GUI already and was the basis of well known applications like Bravo or Gypsy; the original OS and the said applications were implemente in BCPL; and all were operational before Smalltalk-76. By Wirth's first PARC visit in 1976–77, Mesa had already become a self-hosting systems-development tool (small operating system and symbolic debugger); I'm not aware of any substantial Smalltalk influence at that time.