SunOS 4 was still BSD-based. You can find the source code for SunOS 4.1.4 on TUHS's code comparison site[1], but for some reason, you can't browse the tree.
Solaris was when Sun made the jump to System V. AFAIK part of that was because Sun had financial difficulties at the time and AT&T offered to help them -- in exchange for Sun to rebase on System V.
Solaris was when Sun made the jump to System V. AFAIK part of that was because Sun had financial difficulties at the time and AT&T offered to help them -- in exchange for Sun to rebase on System V.
[1] e.g. https://minnie.tuhs.org/cgi-bin/utree.pl?file=SunOS-4.1.4/us...