I understand you're looking for a guide on Windows 10 version 1603 (which doesn't exist as a standard release — the closest are 1507, 1511, 1607, 1703, etc.). You likely mean (Anniversary Update) or 1703 (Creators Update).
A "repack" is a modified version of the operating system created by a third party. Downloading and installing repacked ISOs from unofficial sources is strongly discouraged for the following reasons: Malware & Backdoors windows 10 1603 iso download repack
The search for a "Windows 10 version 1603" reveals an interesting reality: The Mystery of Version 1603 I understand you're looking for a guide on
An enthusiast may have labeled a highly customized, unofficial build with an arbitrary number. unofficial build with an arbitrary number.