I'm trying to install El Capitan on E5420 and getting the same issues as you were... but I'm not sure exactly how to run this script to fix the issue?
I was able to copy the .dsdt and origin folder to get a bootable USB and was able to run the installer. But... I can't get the installed OS to boot, tried -x now working....
I get a panic right after com.apple.xpc.launchhd[1] <Notice>: Extension SDK cache is not present.