V6's use the same K-member as the 5.0, but not the 4.6L
In other words, if you want to convert a 3.8L to a 4.6 you'll need a new K-member, but if you wanted to convert it to a 5.0, you just need the new engine mounts.
The 3.8L and 5.0L share a lot of similar dimensions and mounting setups.