If the recommendation was just because everyone is going that way then why is this particular airplane one of the very few with that recommendation.  The have many other P-51s that don't say that.  Now, while I appreciate the comments I wish someone who really knows the answer would respond?

BTW, remember when "everyone" was switching to narrow band?  Remember that it took years for that to happen?  People don't jsut throw away a $300 radio because "everyone" is switching.