This is the same of my guardian farm and I replaced the blocks. When you place it you will be standing on the sea lantern at the two doors seen on the main picture, so you will want to stand in this position on an ocean monument in your world. You need to AFK around 180 blocks above the center to get good spawn rates.
Revision: I made the water flow different, it appears to flush mobs better. Moved two pillars over one space and added glass front.
Added a storage area with most all crafting tools, layered down to an auto farm for veggies along with an iron farm / trading with villagers. If you have access to world edit you can supply villager eggs. In the auto farm you need to supply each of the four farmers with eight stacks of their farming veggie. One get tators, one carrots, another gets wheat seed, last gets beetroot seed. I set a chest with eight stacks of what they will be farming, once they choose their craft I break the chest and the farmer grabs the product. I have absolute confidence World Edit will fubar the rail systems in the guardian drop collection area and in the auto farm area. Each of the two rail systems has a trap door setup to allow you to get in crawl mode to repair the railing.
(Edited this text to the upgrades. Note to self "don't post anything at 3am after too many drinks")