custpacks can be found in the download section of TopSony, did you look there?
I believe only FarManager/Jdflasher is the only option for flashing CID53, the tutorial you have should work fine. I've seen another somewhere without the screen shots that I've followed which worked too, but can't find the link.
You need to select "babe" when flashing MAIN and FS.
OK found it JDflasher Flashing/Debrading/Customization Tutorial/Guide | Sony Ericsson Flashing