DPF Help

[Igor58]

Got pete 386 3 years ago, with ISX CM871. It was used with 410,000 miles on it, de-mandated, replaced original turbo at 760,000.
Found that site and after reading a lot on forum did some things that you guys advised - EGR tuneup,oil pump shimming. Decided today to check DPF canister and DOC. Remove it and not sure what to do. DPF canister got couple holes thru it, DOC intact ( no any holes, just little bit ash).
Because it de-mandated I heard that DPF must to have big hole, but what about DOC? Why it intact? And how much ceramic I have to remove - to the bare metal or just make hole 8-9 inch and leave it.
Sorry if asking not in right place.