Machina Fortress (2x)
A VERY strong extender, and can dump Graveyard Infinitracks for later plays, and is quite annoying to remove, as targeting it with a monster effects will lead to a hand-rip, or being destroyed by battle lets it pop an opponent's card. It's Summon is also inherit, meaning it cannot be chained to until it already hits the field.
Machina Air Raider (1x)
In case hand goes horribly wrong, this guy can Summon any Machina from the Deck with a lower Level than it, and destroys itself, which again, triggers Citadel's effect to use as disruption.
Super Express Bullet Train (1x)
Helps extend plays, retrieves combo starters during the End Phase.
Ancient Gear Box (0-1x)
Searches an EARTH Machine with 500 ATK/DEF when itself is searched, which then it can be discarded for other card's effects.
Spells
Heavy Forward (3x)
Searches an Infinitrack on activation, and can attach itself as material later on, acting as another 3 copies of Harvester.
Machina Redeployment (3x)
The "Discard 1; search 2 monsters" Spell card for Machinas, used to fetch Citadel and Fortress to extend plays past River Stormer. Although there are only so many targets for it to search, it is worthwhile to run 3, as the endboard we can make far outweighs the drawback.
Urgent Schedule (2-3x)
Summons 2 EARTH Machine from the Deck if the opponent controls more monsters than us. The best turn 2 card which initiates a massive combo depending on your hand. Summoning Harvester and Trencher is usually ideal as it can immediately be linked off to get bodies and reviving Harvester to combo as usual. Can also serve as fodder for staples.
Outrigger Extension (1x)
Protects the Machine Xyz monsters from targeted effects, making them even harder to remove. Used to Rank-Up Infinitrack Xyz monsters to a Machine Xyz whose Rank is 2 Ranks higher than the one used as material.