Getting the modules into the PREFIX path is not the problem. It is ensuring that the modules is installed in the correction location w/in the PREFIX path that is the problem:

PREFIX=/usr/local/perl5.8.6

/usr/local/perl5.8.6/lib/5.8.6/sun4-solaris/Errno.pm (core)
/usr/local/perl5.8.6/lib/site_perl/5.8.6/Errno.pm (cpan)
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First off, thanks for all the feedback so far. 'Errno' is an example of one such module. This modules was installed as a core module to: /usr/local/perl5.8.6/lib/5.8.6/sun4-solaris/Errno.pm

When I use CPAN to install this module, it defaults to installing in: /usr/local/perl5.8.6/lib/site_perl/5.8.6/Errno.pm

I tried to specify the following arguments that would be passed to Makefile.PL to adjust the install path: 'makepl_arg' => qq[INSTALLDIRS=perl}

With this makepl_arg set, the module still installs into the same directory.

I did run across a post that suggested specifying the INSTALLPRIVLIB to the value of $Config{archlibexp} (while 'use'-ing Config), which does seem to tell the module to install into the correct location.

So, if specifying the INSTALLPRIVLIB makepl_arg is a possible solution, the questions that remain are:

• Do all core modules specify INSTALLDIRS=perl as their default location? If not, we would have to add this to CPAN::Config which may cause issues for non-core modules.
• If I specify INSTALLPRIVLIB=$Config{archlibexp} in CPAN::Config, could this cause problems for some modules?

Lastly, getting back to the original question, regardless of how it is done, is clobbering the old (core) version with the new (cpan) version of the module the recommended solution? Or would anyone suggest the @INC overlays?