The Earth - Hexed-Sealed Fusion or King of the Swamp can be used as a substitute fusion material in place of Ancient Gear Golem.
As an Auto-Duel Deck, this deck is very linear and does not require much strategy to use.
Adding Ancient Gear Castle to this deck gives you more options to summon your big monsters, but may mess with your Balance.
Fusion Gate can be used as a substitute for Fusion Sage and/or Polymerization, but keep in mind your fusion materials will be removed from play meaning you will have no Ancient Gear Golem in your graveyard to revive.
The risk there is that you do not have enough cards to discard for it to search for polymerisation. You would get a fusion material back on a fusion summon, but how may times do you expect to summon UAG before you win?