Our 357 Formula w/420's has 3/8" hose from tank to filter, our 29 Fountain has 5/8" hose, I'm sure that both are stock for each boat, but does 3/8" seem large enough for a feed line? I think there are checks at the tank fittings, any problems with these? Changing these soon, thanks for any ideas.

3/8 is sufficient for 420 hp. If the lines are getting old and hard and you are going to change them, then go with at least 1/2" for any future engine mods. I would also remove the anti siphon valve. They do restrict flow and I've seem them start to fail with age. They will start to flow less and less fuel over time. Hope this helps, Eddie.

Eddie, without electric fuel pumps, will it take some cranking to get fuel back up to the carb after it sets for a week or so ? If it doesn't cause any problems, sounds like the way to go. Thanks for the reply, Bob

As long as there is fuel in the carb., it will fire up without any problems. It will take much more than a week for the fuel to evaporate from the carb bowls. Once it fires, the pump will fill the bowls up quickly. So, you should have no problems with that setup.
Eddie