Lifters should pump up if there is oil pressure. If they are shot, they may not pump up, but would still send oil up the push rod. Did you stuff the tips of the push rods full of Molly break in lube or grease? There is not a lot of oil pressure or volume in the push rod. Chevy push rods are almost always coked up to the point of almost being blocked by 200K. I've seen them where you can't even see light through them.
Old school stock lifters use to send a lot of oil up top, performance lifters use to have a smaller office to send less oil up top, as you could suspend about a quart in each head at sustained high RPM's. Im guessing marine engines are designed for a "tractor" application (constant rpm) high rpm at that, that they may have lifters which limit top end oil volume.
Chevy oiling from the pump, to mains and up to the cam, the distributor has an upper flange (about midway up) that seals an area to send oil to the lifters. If you ever "primed" an engine there is a tool that resembles a distributor shaft that you can spin with a drill to pre-oil an engine prior to start up. If you try this with a ratchet extension and coupler it will make oil pressure, but not at the top end, no mid seal to pressurize the lifter galley.
Before I did lifters, I would pull the intake and use an oil pump priming tool and see what's going on at the lifters.
