Ford has "recommended" Motorcraft syn-blend oil for at least 20 years, and millions of vehicles with billions of miles have used "conventional" oil with no issues.
As said though, a SN+ (and most SN) oil is a blend (since there is not definition of blend, there is no way to know what percent is what), so you are fine, especially with the Havoline box, it is a very under-rated oil.