Oh hey, that totally sounded familiar :) Pretty sure this is from Konyok Gorbunok (The Little Humpbacked Horse), a 1975 Soviet cartoon based on a famous Russian fairy tale. The bit you're describing is at 1:07:30 of https://youtu.be/fKc22eSL1gA.
This doesn't quite fit several of the points you remember (very much in line with the post!), so perhaps it was some other edition of that same story.
EDIT: so, I just plugged your description into ChatGPT and it gave the exact same answer, including an identical timestamp! Weird.
The heirloom I have is a small rug and it has horses and riders on it, with pointy boots and shoulder pads. So I'm guessing that's where the overlap came in but yes, this is it! It's "The Magic Pony" and the English version is online too!
I also didn't remember it as being an hour long. This is so exciting! Thank you!
> EDIT: so, I just plugged your description into ChatGPT and it gave the exact same answer, including an identical timestamp! Weird.
In my defense I pasted my post into chatgpt before posting it so that this wouldn't happen, and it suggested "The King's Daughter and the Three Cauldrons" and "The Three Brothers".
Haha, you're very welcome. The ChatGPT thing is odd in how close the answer was to my comment, including specific words I used. Makes me wonder about the likelihood of it being scraped and processed by OpenAI in the 10-15 minutes between posting the comment and trying it in ChatGPT. Or perhaps our brains are just LLMs after all :)
This doesn't quite fit several of the points you remember (very much in line with the post!), so perhaps it was some other edition of that same story.
EDIT: so, I just plugged your description into ChatGPT and it gave the exact same answer, including an identical timestamp! Weird.