How to install a specific version/build of Safari?
I do not think you can find level of builds for Safari. As long as you are running the current latest version of Sierra, You will have the latest version of Safari.

To find the latest updated version and patch details you can track them on Apple Support.

The last updated for Safari came on 15 May 2017 - Safari 10.1.1

Supported OSes - OS X Yosemite 10.10.5, OS X El Capitan 10.11.6, and macOS Sierra 10.12.5