how to downgrade from 4.86 to 2.80

Hi guys
I have a stock 60gigs Backwards compatible Playstation 3 sitting on 4.86 firmware.

I was thinking of going back to 2.80 firmware well for nostalgic reason & leave my 60 gigs on there for a foreseeable future.

Is it safely possible to do so? If yes, what is the procedure?
Thanks.