I am looking to replace the engine (5.4) in my '99 F150 4X4. I have found a really good deal on a rebuilt, but I'm curious if there's a way to tell if the heads have been updated to correct the spark plug blow out issue.

 

Depends on who you get it from. In my experience, all off the shelf rebuilt engines are what I call budget rebuilds. They often do not update parts, they usually only fix what cause the motor to fail int he first place and maybe a seal kit. What prohibits you from having your old engine rebuilt? A proper rebuild is usually better than a new engine.

If your rebuilt motor comes from a smaller private firm instead of a national rebuilder, the chances that it is good are better. But even so, it really depends on who did the build. As you say its a good deal. That tends to imply that corners were cut.