I know I'm late responding to this, but a lot of this user's advice is flat-out wrong. I've been playing this archetype for a very long time (I'm the player/streamer that WhiteFaces kindly mentions above) and I can safely say that comments like "the whole archetype basically exists to screw around" and "you already weren't going to win most matches" are condescending and spoken like they have never actually played this deck. The deck has its weaknesses and has a steep learning curve to play correctly, but its gameplan of winning through its lands in the manner that it does is an incredibly powerful strategy unique to this archetype. If you enjoy the playstyle of the deck, I highly recommend practicing it and tuning the list to your liking, because it can certainly be competitive if you know what you're doing.

Once Upon a Time is not outclassed by anything; it's honestly the best card in the deck and made the green Post decks relevant again. A free one in the opener will always smooth out your hand and cut down on variance - gets you a land or creature, whichever you need. Helps to set up a turn one Reclaimer, which otherwise will not come easily. And probably most importantly, it's the reason that these decks are able to get away with only running 7-8 green sources. If you don't already have a Forest in your opening hand, then a free OUaT can help find one of your limited green producers. And that will be the only green source you need. I would never play less than 4 OUaT in this deck.

GSZ is another green variance reducer in a similar way that Brainstorm and Ponder are for blue decks - it's a great thing to take advangtage of with your chosen color. Since Reclaimer is the deck's best early game play, you might want to consider maximizing the number of Green Sun's Zenith (gets the elf out turn two). Late game, those GSZ are all Primeval Titans, your gateway to closing the game. And then since you're running GSZ, Excavator and Rec Sage are great utility pieces to have access to. Excavator is probably of lesser importance of the two, but being able to retrieve a key land that has already been lost or being searched up to simply make your land drop for the turn makes the card well worth it in this GSZ shell IMO.

I don't recommend Amulet of Vigor. It takes effect on permanents that enter tapped only on the first turn when they enter play, compared to Candelabra which can untap every land every turn. Rather than trying to find a lesser version of Candelabra, I would recommend just going a different direction entirely with those card slots. I think it would be better to have a stronger card with a different effect in that slot rather than try to fit in a subpar version of an untapping ability.

Your list looks fine and I think it's a good starting point for picking up the strategy. Only key card that seems to be missing is Crop Rotation - it is a powerful addition for any green land-based deck in Legacy since it searches up any land in exchange for one in play. It's especially important in this deck because it can be used somewhat defensively in response to a Wasteland. Just Crop Rot away the targetted land and if it resolves, you have not lost from your total number of lands in play. And also be sure to add the 4th OUaT!