Ok, so my summary is this:
My inferred question about how SunOS 5.x and Solaris operate together
(which amounted to asking how bread and pb&j sandwiches work together)
was succinctly answered:
Solaris 2.x = SunOS 5.x + goodies
And, a list of the resources for which I'm grateful (though as yet I've
only checked a few)
http://smc.vnet.net/solaris_2.5.html (Solaris Freeware - nice)
http://www.gnu.org/order/ftp.html
http://www.gnu.org
http://gamma.magnet.fsu.edu/download/gnu
http://www.stokely.com/unix.sysadm.resources/faqs.s.html#faq.link.sun
http://www.stokely.com/unix.sysadm.resources/shareware.www.html
http://www.cnt.ru/~ftp/
ftp://prep.ai.mit.edu/pub/gnu/sparc-sun-solaris2/
ftp://prep.ai.mit.edu/pub/gnu/solaris
ftp://sunsite.unc.edu/pub/gnu/solaris-pkgs/
ftp://sunsite.unc.edu/pub/solaris
ftp://ftp.lanet.lv/pub/unix/solaris2/
ftp://nic.switch.ch/mirror/gnu-sparc-solaris/
ftp://ftp.quintus.com/pub/GNU/sparc/
ftp://uwsg.ucs.indiana.edu/pub/solaris/binaries/gnu/
ftp://ftp.fwi.uva.nl/pub/solaris/solaris2.html
ftp://ftp.cnt.ru/pub/unix/solaris