I hand carve that style tip for a lot of aircraft. Its amazing how much they improve some planes.

Start out like you're going to make a carved rounded tip out of a rectangular block of balsa.
Tack-glue (or screw) the block on the wingtip. Have the top edge of the block run along the top of the rear 2/3 of the tip rib.
Carve the forward 1/3 and upper half of the rest to match the airfoil, and mark the airfoil on the lower inner side of the block. Remove from wing.
Carve a smooth curve from the lower outside corner in to the airfoil line.
Carve the upper rear section curve, letting the section get thicker as you move from the lower corner, up to the upper airfoil shape, and round out the forward portion.
Sand smooth. A dowel or piece of broomstick wrapped with sandpaper is very handy for the inside curve.

If desired, you can hollow out the block to cut down weight. Or you can sand the tips down a bit more, seal the wood grain and use them to mold fiberglass tips. (getting the glass off in one piece is hard... Usually have to split the trailing edge to do it.)