I'm building a 540 I currently have a mechanical pump driven off the seawater pump which fed the high pressure pump for the efi. Looking for ideas on what kinda pump to run and how to plumb it. New engine is carbed and going to be somewhere in the 600-650 hp range. Electric or mechanical off the sea water pump and if I go with a mechanical pump which one should I use and should I run a regulator. If so should I run a return style regulator? Thanks for any thoughts. I was thinking mechanical would be more reliable but looking for thoughts.

I'm currently running the Airtex version of the Merc sea water pump and I'm running almost 700hp. You don't have much of a selection when it comes to the sea water pumps as they have a different cam follower than the block mounted pumps. All the pumps I've found don't require a regulator. I do recommend -8 lines from the tank to the carb. FYI, don't get the Keith Eckert valve body upgrade, it's junk.

I would put a Weldon 1100A and a return regulator on it and call it done. Plenty of fuel pump if you want more power later, also works great on EFI

I don't think the 1100A is Coast Guard approved. You would have to use the DB2025-A.

Does this pump pull the fuel from the tank or does I need to be mounted close to the bottom of the tank?

It will pull fuel a long way, but I would mount it as low as possible. I mount them on the front side of the offshore type motor mount and have never had an issue