In any case I would definitely look into backing these up for you personally.

I am not too fond of the idea of pumping old reddit content out onto lemmy (you couldn’t recreate the entire threads by yourself anyways).

BUT, I too have a post or two that I like a lot and would love to be on lemmy too. I know it’s a bit more work, but maybe create a summary post of the topic in a fitting sublemmy. That way you do transfer the knowledge and make it accessible again AND you create a new high-quality piece of content for this community. It may not be new to the world, but it will be new to basically anyone over here! Reddit is so vast, stuff just gets buried and most people never saw it.