Here is a list of useful links to good MTG Old School content:

The 3 biggest OS formats are:
http://oldschool-mtg.blogspot.com/p/banrestriction.html
https://sentineloldschoolmtg.com/atlantic-93-94/
https://www.eternalcentral.com/9394rules/

A couple of interesting takes on regular OS:
http://northernpaladins.com/paladin-magic/
https://beastsofthebay.com/old-school-type-1-5

But there are a lot of others. Check out this link to see all the differences:
https://ligaoldschoolmadrid.wordpress.com/2018/08/30/picture-of-variations-in-old-school-rules/

Noteworthy links and blogs:
https://www.oldschoolmagic.nl/
https://ragingbullseries.com/
http://oldschool-mtg.blogspot.com/
https://ancientmagicthegathering.blogspot.com/
https://www.wak-wak.se/
http://alltingsconsidered.com/
https://brothersoffire.home.blog/