This is a good drink but Im not sure how much the brandy is contributing. And I know the grenadine is only contributing a little sweetness and a little color. The fresh lime juice is however contributing to balancing the drink against the 7up sweetness.

So 2 oz Rum/Brandy/Whiskey with a good sized wedge of lime juice and 7up is a winning combination.

Basically a 7 & 7 like @Dump-truck suggested but with some extra fresh squeezed lime juice.