you need the ofw but u don´t need to dump it..
the tut for downgrade is a littel out of date so i updated it a littel:
Step 1) Copy the version.txt to "ms0:/seplugins/....(version.txt)"
Step 2) Copy xHENx example 6.20 TN-D (e) or other hen to "ms0:/PSP/GAME/xHENx/...(eboot.pbp)"
Step 3) Start xHENx.
Step 4) Press select and turn "Fake index.dat" on enabled.
Step 5) Copy now OFW 5.03 to "ms0:/PSP/GAME/UPDATE/....(eboot.pbp)"
Step 6) Start now the OFW 5.03 updater and update.
Step 7) Voila youre done.
read more at the downgrade section or you may brick your system.. make sure you know what you do (example: flash protcetion should be turned off)
^^thinking for now me reached 3 times the 1000 post