Check the manifest of the implementation jar
Thanks for the reply. Sorry if I was unclear in my original post but, unless I misunderstand you, what you suggest is exactly what I had tried. I cracked open the jar files (both jsf-api and jsf-impl) in winzip and looked at the MANIFEST.MF file for JSF version breadcrumbs. All I found was JBoss references, like:
Implementation-Version: 4.3.0.GA (build: SVNTag=JBPAPP_4_3_0_GA date=2
Which I believe is boilerplate JBoss build version info but I found nothing that looked like a JSF build version.