I think the first point to clarify is whether you have (perl5.8.6 + XS modules) binaries which can not be re-compiled by you or them on the newest OS (and subsequent upgrades). OR whether you have sources: Perl and modules. If Perl sources were not modified and you can use a stock perl5.8.6 then install it with perlbrew. Else, try to compile it in your new OS, that's a straight-forward route, I don't foresee unsolvable problems with compilation (on a Linux system at least). As for modules, if you have custom modules sources that need to be (compiled and) installed, then just do that manually.

If OTOH you only have a perl5.8.6 binary or XS modules binaries but no sources, then tell us. The longshot is that hopefully, they supplied you with binaries-only but these binaries are nothing special but were compiled from stock, publicly-available sources, in which case it is worth to manually compile and install and see if you get any problems in the program output, tests failing etc.

bw, bliako