TRE is not a fly by might engine builder. They have a very good name and build a quality product. It is worth an email or call to Paul just to see if he has any insight about the problem. If this is a 5.0 roller block , there could be other problems causing this . Nascar teams used to "pin" the freeze plugs in the block by drilling small holes for rivets to keep the plugs in place. I like using the Ford racing screw in plugs and have the taps to do it myself. We don't get freezing cold weather in California so I'm OK doing it.
Despite being six years old , I'm sure Paul will help you to figure this out.
'66 GT350H-3 time cover car - Car Craft July'77,Modified Mustangs and Fords Feb2011 ( w/article), Mustang Monthly June 2014. Bracket raced by me for the last 44 years. Yes it is a real one.
'68.5 R code GT fastback
'67 Ranchero 408W -427 glass hood
'78 F350 "Oleynik" car hauler
Ford Experimental parts collector