Adding Google, Facebook, Hubspot scripts when using a custom header

Hello there! I am building a new site for a company that already has a site with facebook pixel, google tag manager and hubspot code in their headers/footers.

I built custom headers and footers using themer which I guess means that I can “customize” the theme in the “code” area where I would normally add these scripts. Where is the best place for me to put these scripts under my scenario? I’d like to be able to use comments above the scripts so I can keep track of what it what.

Thanks in advance for your help!