IMO the engines in question, if in stock condition, are not in any danger if using current "normal" engine oil. And if they were mine I would not concern myself with it. OTOH, it certainly won't hurt to buy oil that contains a higher level of scuff additives.
The above is the summary; below is the long version!
I am aware of all the issues (real and imagined ) re this subject but it basically applies to non-stock, modified performance motors. I assume, perhaps incorrectly, that the 454 engines in question are stock and unmodified - at least as far as the valve train is concerned. They are anything but performance engines (that's a GOOD thing in the marine application).
Virtually all of the issues with flat tappet cams/lifters has occurred relatively recently. The reality is that flat tappet cams/lifters are NOT made to the standard that they were years ago when they were part of the "normal" OHV valve train. Most of the US makers of flat tappet cams/lifters quit making them because there was no longer any money in it because, as noted, nobody uses flat tappets in OHV engine manufacturing anymore. Some cam makers now supply flat tappet cams/lifters that use dissimilar materials (!) made to a low price point. They used to grind/produce their own, now they import them (from guess where) because there is no profit in making them since there is very little demand. Performance/competition cams have been dominated by roller cams for MANY years and now that's the standard for any OHV production engine.
We used to get examples of wiped cam lobes quite regularly - even back in the old days - on engines that had been modified but the cams were improperly broken in. I'm not saying that the issue nowadays is due to a spate of poor break in - which can ruin a cam in 1500 miles or less - but the fact is that less than adequate break-in coupled with lesser quality cams/lifters may be part of the deal.
I totally agree that there must be "special" lubrication, for current flat tappet cams/lifters. IOW, if you buy a new flat tappet cam/lifters from say, Comp Cams, you will need a higher than standard level of scuff additives than some oils provide. But the motors in question here are not in that category UNLESS the valve train has been modified.
In any case, as noted earlier, if additional ZDDP is needed, an oil with the necessary amount of ZDDP already in it should be used as opposed to pouring a bottle of goop into the engine oil.
