Looking for information on my manual valve 904

I am just looking to gather information on my tranny. Im 29 years old and love muscle cars but they are not from my generation.

I recently bought a 72 Swinger. It's got a 3 speed tranny that is a manual valve body tranny. I was told by a local tranny guy that this is basically a set up for drag racing. My car has a nice running 318, but I wouldnt say that it is much of a racer.

I am asking what the positives/negatives of this are. Are there any benefits to a manual valve body kit?