iPhone 3G 3.1.3 restore only

[marchingant]

I have an iPhone 3G 3.1.3 NOT jailbroken but I recently bought an iPhone 4 and I want to restore the phone to sell.
When I click to update in iTunes it of course wants me to install 4.1 which I have no desire to do (let the buyer decide).
I downloaded 3.1.3 off the net, is it as simple as just Shift+Update select and select the downloaded software (3.1.3) and it will restore to that exact software because it is installed or do I need to do DFU with RecBoot?

Thanks.

[iYeow]

Yes, as simple as shift + restore, no dfu no recovery and you will have a fresh os 3.1.3. You don't need recboot.