Now that I've got a 360 list, I can make changes with 1 to 1 swaps.

An Offer You Can't Refuse => Filter Out

• I never really wanted to have too many counterspells in this cube, and a narrow one like An Offer You Can't Refuse is nice when you need it, but it can feel pretty useless in a creature heavy environment. Filter Out lets you deal with artifacts, enchantments and walkers for a turn, giving U/X decks a chance to stabilize in the midgame.

Old Gnawbone => Wolfbriar Elemental

• Old Gnawbone really doesn't fit. It costs too much mana, and green was already too top heavy to begin with. Wolfbriar Elemental gives G/X decks a mana sink in the late game and slots in nicely with G/W token strategies while evening out green's curve. (I didn't want to buy or proxy Old Gnawbone anyway)

Fable of Wolf and Owl=>Hydroid Krasis

• This was a pretty simple swap. I'm still trying to figure out what to do with simic other than just being valuetown. Fable is just a little too slow for the cost. Hydroid Krasis can help stabilization and give players something to cast in the late game that can give them gas to go for a win.

Etched Familiar => Ebondeath, Dracolich

• Evening out black's curve. Etched Familiar is neat, but Ebondeath will allow black decks to always have a creature to work with for various strategies, or just as a recurable threat.

Generous Gift => Sky Crier

• This swap hurts a lot, it might be temporary. White has too much removal at 3, and could use more mana sinks and card draw. Sky Crier does this and more. Generous Gift might come back later, but not in Sky Crier's place.

Mukotai Soulripper => Underworld Connections*

• More curve evening. Mukotai Soulripper seems too slow for arisocrat strategies, so swapping for more card draw to keep the games moving.

Dodgy Jalopy => Esika's Chariot

• Just a power upgrade. Going forward the bar for vehicles will be higher. I love them as a concept, but they need to be draftable by any player, not just someone leaning into vehicle synergies.

Lifecrafter's Bestiary => Abundance

• A conceptual swap for the later points in the game. When you don't want lands anymore, you won't get lands anymore. Should be helpful against late game stalls in G/X.