What Sherman said, just asking for trouble if your running it that hard consistently. If it's turning that high and everything is in order you are under propped ( to low of pitch )
WOT early flat tappet cam 5.7L
4400 - 4800 RPM's.
https://www.amazon.com/Scepter-Marine-Brass-Siphon-Valve/dp/B01BNBEF64/ref=asc_df_B01BNBEF64/?tag=hyprod-20&linkCode=df0&hvadid=312094677816&hvpos=1o4&hvnetw=g&hvrand=1031204924829857041&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9005656&hvtargid=pla-570810915055&psc=1
or similar , brass is the better option over the aluminum version
https://www.google.com/search?q=marine+anti+siphon+valve&oq=marine+antisiphon+&aqs=chrome.1.69i57j0l5.18448j0j8&sourceid=chrome&ie=UTF-8
Lets not confuse this issue anymore than it has to be Cornelius Both do the exact same job and that is letting fluid flow in one direction only. They might do it in a different internal manor but they both do the same thing. The anti-siphon valve that screws in the tank and that can also be used off a water separator for the kicker feed utilizes a light spring, ball & seat to seal any back flow at all times unless there is vacuum draw on it. If there is no draw on it it is sealed closed on the seat as not to let fluid/gas siphon out of the tank hence the name. There are other styles of check valves that can be used as well but the anti-siphon tank style valve fits the bill in many cases.
Check valve / anti-siphon are basically the same, you will be fine using one off the water separator to the kicker along with the one on the main tank .
Put one of these engines in it & your ready to go >
https://www.lakeontariounited.com/fishing-hunting/topic/76633-pair-of-350-volvo-inboard-motors/?tab=comments#comment-568209