What Holley multi-port injection system are you running on the 7.4's?

yep

https://cimg9.ibsrv.net/gimg/www.off...8419b7db87.jpg

Holley HP with old Cutler multi-port intakes, D585 coil CNP.
https://www.offshoreonly.com/forums/...onversion.html
https://cimg2.ibsrv.net/gimg/www.off...529f71eae4.jpg

A 500 efi uses same exact fuel pump as a 502 mpi, a 190 lph

They had different part numbers when I looked them up.
It would seem then that he has sufficient fuel supply for that hp goal

I had stainless marine make me larger cool fuels, the problem with the 500efi ones is the 90* fitting that goes down to about a 1/4 inch... ASM made a -10 U bend that works great. with an aeromotive pump i was able to make it all as a nice pkg that bolts right in the same spot as the 500 efi, return goes right to the filter.

I stand corrected, there both 210s, from going on dyno data, dont know how I came up with 190, getting old, the pigtail;l on a 454/502 mpi version is about twice as long, only difference that I know of, but always learning new stuff and thats my guess, might be wrong.. Ive gotten to around 580 to 620 observed hp depending on BSFC/afr before running out of fuel pump with stock pumps on both 502s and 500 efis, Ive yet to find any bigger aftermarket pump that has that stupid female push in end where it could easily go in place with no other mods, Smitty
210 lph x 1.63 + 342 lbs hr with good voltage, pump thats not weak etc. at .500 bsfc would get you to 680 hp, most these 502s/500s run about .550 bsfc on top so take about 15% off that then you see will get to about 580/ 600

SO to update I just placed my order for the Holley injection system and this is what is coming:

HP EFI #550-604N
6EFI coil #86415
6EFI ingition box #6415
Dual sync distributer #565-200
Intake & rails #300-563
Throttle body #112-588
Injectors #522-488
Fuel press reg #12-846KIT
Reg bracket #20-259
Fuel pump #12-920

My question is the return line, I know it can go back to the fuel filter but I would think over time that's going to add a lot of heat to the fuel lowering the fuel coolers efficiency or am I overthinking it? I wanted to return back to the tank but I am not taking up the tank to clean and weld in a return bung. I know I saw that I could return into the fuel tank filler but not sure thats a great idea I was wondering if I could modify the fuel sender and add a dip tube to return fuel back to the tank?

What water neck is that? I would like to update the stock MPI water neck currently on the boat.

Stainless Marine that came with a crossover. I made a 1/4" aluminum adapter plate so I could "clock" the thermostat housing properly. More visible in this pic.
https://cimg5.ibsrv.net/gimg/www.off...521b7e2126.jpg