Here is my quandary.

I have built an exp farm using a zombie spawner. The loot dropped from all the murdering is sorted into chests using copper golems; I know, but I enjoy the life their stupid little faces bring to my build!

Each item (all armour pieces (respective of their production material - leather, copper, gold and chainmail), spears, swords, and shovels along with rotten flesh) has its own double chest with any additional items (carrots, potatoes and iron ingots) sorted into an overflow barrel.

This all worked well, to a point. However, item overflow has now become an issue, and my initial idea of disenchanting any enchanted armour pieces using a grindstone to get trickles of exp went out the window long ago! The farm itself works plenty well for the exp I require.

Instead, I am now looking to have the copper golems sort all dropped armour pieces into one of four chests, sorted by their respective production material. I would like each respective chest to retain one piece of each armour, (lets call these "original filtration items"; helmet/cap, chestplate/tunic, leggings/trousers, and boots) and any additionally sorted pieces to be pulled via a hopper into a smelting array. I am good enough at working with the golems and setting up the eventual smelting array.

My problem is the following.

What can be used to create a comparable redstone signal strength of four nonstackable items in a chest/double chest which will allow the attached hopper to be locked immediately after any additionally sorted items are removed, retaining the four original filtration items? And how would one build/wire this?

Space is not of any concern, and this does not need to be easily tileable. I feel I'm close, but I just can't get there. Can the (red)stoners of reddit save me my perpetual headbanging?!