although it doesn't show well in the picture we do have about a 18 inch lead in. Unfortunately we had to go that deep to get enough water pressure for both engines. I only run 1 very large sea strainer.
https://cimg9.ibsrv.net/gimg/www.off...fb275883bd.jpg
https://cimg2.ibsrv.net/gimg/www.off...4bffc50ccf.jpg

What size water line are you running?

-20 from pickup to sea strainer then -20 out to each pump.-20 to bell housing then 2 -16 to cross over. 2 -16 from intake to exhaust.

Is a -20 big enough for both engines?

1 1/4 inch hose. Yes same setup that they use on the race boats. A friend owns the kilo boat it is set up same way except pickup is on the back step.

measure the fittings they are smaller than the hose size by a fair amount. I'd run 1.5 inch hose.

your pickup looks deep and big, so I'm thinking your restricting flow after that.

Yes it does look that way. But that is the end result of achieving what we were after. Our water pressure doesn't vary more than 3 or 4 pounds from 30 mph to 110 mph.
I may loose a few mph but that's ok with me I would rather have the steady pressure.

https://cimg1.ibsrv.net/gimg/www.off...334bcec45e.jpg
The hose connected to the shutoff valve is an air bleed. It exits low on the side so when the boat is off plane it is underwater. That way it doesn't suck air. When under way it bleeds any air that is in the strainer. You can fine tune your pressure by the size restrictor you use in the hose. When we are going it pushes water out this is how I am sure we have enough flow.

https://cimg1.ibsrv.net/gimg/www.off...199a911a5e.jpg
https://cimg3.ibsrv.net/gimg/www.off...49443a65b7.jpg
https://cimg4.ibsrv.net/gimg/www.off...0a5962380f.jpg
a few pictures of the engine bay