My Holley red pump wouldn’t even keep up with my stock 454 with mostly straight fittings. How well it would work in conjunction with mech pumps is above my pay grade. Those look like 3/8” fittings which seems marginal for a 540.

7-8# of pressure is good but that just means the flow into the carb can be a restriction at the needle seat, or however these carbs are built. You can have full pressure on the line and still suck a float bowl dry.

As near as I can tell someone stuck big power in this boat, probably got frustrated with not getting them to run well (didn’t upsize the supply side), and sold it?

I had zero interest in becoming a boat mechanic and searched for the best in my area, and I really liked the guy, but just by the help of the OSO brain trust here I learned a ton and realized that he knew nothing other than replacing oem parts, which is fine for 99% of what rolled through his door. Most marinas will have the same level of talent at best, I imagine. It sounds like you’ll be in good hands now.