2nd Generation iPod Touch Downgrade

Hi, I have a 2nd Generation iPod Touch running iOS 4.2.1, and I am wanting to downgrade to iOS 3.1.3 or earlier, simply to speed the device up and I have this iPod more because I collect them, and to me it's more authentic with iOS 3 or 2. I am receiving the iTunes error 1646 when trying to restore with the older firmware (I have the firmware on my computer as I used to back them up, I backed it up when 3.1.3 came out). Thank you in advance