The A pillar pieces just stack up like a sandwich, so the trick is to carefully use a panel cutter air chisel with a thin section cutting tip and slice them apart. A thick, sharpened putty knife with a full tang can also be driven between them. Sometimes you can drill out some of the spot welds to make the job easier, but it's time and patience that does the job. As you mentioned, take a good look at that cowl/firewall since a hole 1/16" big will soak your carpets and rot your floors. These cars are notorious for it and where you see one, there'll be 3 more you don't see right off the bat. Not trying to bum you out, but it'd be a royal PITA to fix SOME of them, paint it and THEN discover there's more. Ian