If you already have Windows 7 SP1 64-bit installed but cannot get Windows Update to work (common error 0x8007000E), you do not need an ISO. You need the offline installer.
Since there isn't an official SP3, we will focus on creating and using an ISO for a fully updated Windows 7 64-bit installation, incorporating SP1 and the Convenience Rollup. windows 7 service pack 3 download 64-bit offline iso
Official Microsoft support for Windows 7 has ended, and importantly, If you already have Windows 7 SP1 64-bit