The Mighty will be for more medium-heavy conditions. Not a true heavy oil ball with the OOB surface, from my experience. The gusto will be more for lighter oil, and when the shot breaks down.
This combination should be a decent asym 1-2 punch for THS. I've always let my PSO decide my layout, but Mo layed out my Mighty and it does well. Too bad I cant remember the angles off the top of my head. But your pap is dead on mine.

Long time reader, but I rarely respond to posts.  I just happened to notice this post today.  The Guru Mighty and the Gusto are the only Radical balls that I own.

I would say that the two balls compliment each other well for Medium Heavy to Medium Light lanes.  The Mighty is a very strong ball, but don't expect too much from it on a heavily oiled lane.  When the lanes are oiled and there is some backend, the Mighty is "money".  LOL.  It is literally one of the best hybrid balls on the market.  Period.  It is very driller friendly and comes back from anywhere on the lane.  IMHO, I should have bought two of them.  LOL.

As for the Gusto, it just can't handle as much oil as the Mighty.  I tend to use mine on the Medium to Light condition.  However, it is not a dry lanes ball.  On the burn, the Gusto will look like someone kicked it to opposite gutter when it hits the dry. 

Both balls hit like a truck on their preferred condition.  As for drilling, I think you'll be happy with whatever you choose.  And especially with the Mighty.  Mine is drilled with the pin above the finger bridge and the MB is about half way between the thumb and the VAL with no balance hole.  My Gusto is drilled with the pin about 3/4 of inch to the upper right of my ring finger with the MB about an inch from the thumb.  There is a balance hole near the PAP. 

IMHO, the two balls are great one-two punch on a THS.  You should be just fine with the two.  Good luck and God Bless!

Peace!