Take a look at Catalyst and see if it would be suitable. I recently spent 4 years working on an outdated hand-coded CMS that started back in 1996 and I understand your angst. I'm just starting w/ Catalyst; it looks like a good choice to me.
Update: "outdated" was not the most accurate description there. It handles constant updating to 200 websites, getting 40 million unique visitors per month, and over 250 million page views per month.
With four Perl programmers, we were quite busy making requested mods, bug fixes,and content updates.That kept us plenty busy.
So the better term would have been "not modern." Especially since Modern begins with 5.10. We did switch up to 5.8 during that time.