There are 6 ways to roll 4 of a kind each with probability (1/6)4, i.e. probability (1/6)3.
There are 6P4 ways of rolling 4 different faces in 4 rolls each of these ways has probability (1/6)4, i.e. probability
360 * (1/6)4 = 60 * (1/6)3.
Therefore, you are correct.