Field Usage points to JPAN's code -- always 161521. The offset to your script has to be added with a hex editor.
(Items all have some extra space at the end of their data; when using JPAN's hack, you put the script offset in that extra space, and JPAN's code checks that space for it and runs it. Unfortunately, I don't know of any programs that let you edit that extra space. Check the section of the tutorial that dealt with the hex editor, and try the instructions again. If you still have problems, feel free to ask me for more help.)