Well, lately I've found old shoujo manga extremely enjoyable and entertaining, so I was hoping to get some recommendations, especially manga from the 70s and 80s, if possible. Historical settings are a plus too 😀

Here are some old shoujo I really liked:

Candy Candy
Akage no Anne
Lady Georgie
Versailles no Bara
Oniisama e
Thomas no Shinzou
11-nin Iru!
Orpheus no Mado

Anything and everything by HIKAWA Kyouko

A couple of these are josei or very shoujo-esque shounen, btw. Hope you don't mind. There's nothing on this list that was published after 1995.

Eroica yori Ai wo Komete + spin-offs
Glass no Kamen
Banana Fish
Kaze to Ki no Uta
Zankoku na Kami ga Shihaisuru
Giniro no Kami no Arisa
Marginal
Poe no Ichizoku
Maya no Souretsu
U wa Uchuusen no U
Terra e...
Banana Bread no Pudding
Claudine...!
Shiroi Heya no Futari
Senrei
Sakura Namiki
Patalliro!
Sakura no Sono (YOSHIDA Akimi)
Boku no Chikyuu o Mamotte
Paros no Ken
Kisshou Tennyo
Earthian
RG Veda
Tokyo Babylon + X-1999
Tsuki no Ko
Nemuranai Machi kara
Ijigen kara no Tayori
Shirahime-Syo
Alexandrite
Basara
Bishoujo Senshi Sailormoon
Kanata Kara
Koko wa Greenwood
Cipher
Yami no Purple Eye
Miriam
Lady Mitsuko
Pygmalio
Waltz wa Shiroi Dress de
Kanyou Shoujo (KAWAHARA Yumiko)
Orochi

You might also want to check out other works by the mangaka of the above series.