Quality engines have helicoiled spark plug threads.
The problem with the Ford Mod Engines is that the plug has too few threads in the aluminum.
Here is a dope sheet on the problem:
http://www.fordproblems.com/trends/triton-spark-plug-ejection/
And it looks like Ford doesn’t want to pay to fix the problem, but they no longer use these engines either.
Fortunately better designed plugs running in an unleaded environment need to be replaced way less frequently so steel to Al thread wear doesn’t accumulate as it used to. Valve seat inserts count more than helicoiled plug threads.
Working with a plug in some deep well makes it even more problematic. A poor “ joint “ design doesn’t help. Modular Engine indeed....