You don't have to worry about using the Power Piston in a Marine carburetor. These aren't "fixed" systems and the carburetor will add fuel with increased throttle angle and pressure differential above and below the throttle plates well before the power piston moves up to increase metering area.
So under load the fuel delivery rate increases proportionally. The power piston will cut-in at some point which occurs under heavy load to increase the metering area. This happens at heavy and wide open throttle openings when vacuum falls below the cut-in point of the PP spring.
Marine carburetors typically use pretty "soft" springs in them to help with fuel consumption under light engine loads but I've never seen a scenario where they ran the engines so lean as to cause running issues or engine damage. If you aren't experiencing "surging", power going "flat", detonation, running hot or any other issues then having the power pistons operational aren't an issue.
The way Marine carburetors are set up you'd need to back the jets off more than .064" when eliminating the metering rods. It would be trial and error but the carbs will actually work fine without a power piston in them. I've done this many times to "save the day" with the later CCC carburetors when there was just too much going on with the ECM and related components to get things to work well.
I also run many of our "race" and "max effort" street/strip Q-jets straight off the jets and they are flawless even for street driving.
I rebuild a LOT of Marine Q-jets here and the biggest problems I see with them is folks using kits that don't have the "high flow" N/S assemblies in them and the correct Marine accl pumps. They pumps being supplied (except for mine) have the soft blue seals on them that don't last anyhow and many are the longer automotive pumps. I also see a lot of brass floats being installed which is BIG mistake for them. They do not have the buoyancy to put adequate leverage on the fuel inlet needle to effectively control the fuel level when using the high flow N/S assemblies.
I'd like to have a nickel for every complaint I've had from folks who just "rebuilt" their Marine Q-jet with the wrong parts, or had it done someplace and are having issues with them simply because they used "generic" instead of the correct Marine components in them......