rusted firewall

I have a 96 skylark. Iv been seeing water on the floor. ripped out the floor and found out i have rust holes on the firewall, from the drains being plugged. The driver side leak is to far up in between the dash for me to get to...Any suggestions? Should i rip the dash out? If so...where would i find any info on the dash lol....or something instructional lol...Im kind of mechanical, but never have done anything like tearing a dash out.. Any help would be really appreciated.

Anyone out there?