I know where you're at! After scrapping a box of "stacks-in-a-bath" type generators I got serious and starting surfing uTube. I found ZeroFossilFuel and his group at EBN. These guys are serious about the technology and share everything, I mean everything. It takes time to watch what they've done; from the beginning. Or you can just watch their latest vids. They have several good vids on WFC (Water Fuel Cell) design. The summary is: decide what production rate your engine needs. Design a WFC to that rate. Then build it. Sounds simple but you do need an understanding first. My advice is to spend some time watching videos, taking notes and then make your design decision.
The plate config you take about it just one in a thousand. Back to the first decision, What rate of production do you NEED.
Why do I know this? I've got three 3 monster dry cells on my bench and don't have an engine big enough or that would need what they produce. I had to build a smaller WFC for my 5.7 L engine. I'm trying to sell the big ones to guys who have really big diesel engines. Something that needs more than 6 L/M. Cheers, HHO-ing in N. GA