Sony didn’t want us going back to firmware 3.60, Freeplays made my own installer. Using an encrypted, un-sigchecked dump of firmware 3.60, the 3.60 IPL, and a few modules from the 3.52 updater, you can now install 3.60 again on slim PSPs.

The readme is intentionally hard to understand (written for experts) because of the risks posed in flashing your entire firmware this way. There are no safety checks in place or anything.


— Update — New version released. I removed the old installer from this post; the newest one is here.