I've probably done more experimenting with dihedral and anhedral than most people so here's how it works.

First, looks don't mean anything, aerodynamics do.

Next, for power planes, except for basic trainers where you want to turn the controls loose and have the plane right itself, you don't want roll stability. (The purist will call this neutral roll stability, but it's the same thing.) You want the plane to go where you point it. Believe me, when you start flying another plane that doesn't have a lot of dihedral and stays in the bank you set, you will love it. Full size planes that go from point to point like it roll stable so they don't have to concentrate on flying. We RCers fly back and forth and do acro so we want it neutral.

Third, the things that affect roll stability and roll coupling (rolling when you put the rudder in) are: wing location, high, mid or low; wing sweep, back or forward and dihedral or anhedral.

Stabilizes and rolls with rudder: High wing location, sweep back and dihedral.

Destabilizes and rolls opposite to rudder: Low wing location, sweep forward and anhedral.

Neutral: Mid wing location, straight wing and no dihedral.

A high wing plane needs about 3 degrees of anhedral on each side to cancel out the effect of the wing location and be neutral. Take just about any low wing sport plane like a 4*40 and put it upside down in your cradle and look at it. It's a high wing plane with anhedral. It flies inverted nicely, does outside loops flies fine. This is the same thing as flying a high wing plane with anhedral upright and doing inside loops. Take a high wing plane with dihedral and fly inverted and it's unstable, wants to roll over on you. Do an outside and you have to concentrate more so than with a low wing plane to keep the plane tracking in the maneuver.

If you can fly and want to experiment:

As for converting an ARF, it's not easy. I usually flip over or make a new dihedral brace and use a piece of aileron stock to fill the gap. Most guys are afraid to do this. I will say this, unless you change the dihedral/anhedral to 6 inches on each side, it won't make a drastic difference. You need an inch and a half on each side. Flat is better than nothing, but it won't correct roll with rudder. It will make it roll better.

Also take off the plastic wing tips, as I recall the plane has or cut the tips square and flat. Then stick on some downward plates extending 3/4" below the wing. This will usually cure roll in a flat wing.

Other things you can do:

Cut off at least 1 rib on each side. Works good on 4*'s, too.

Note: Look at any high wing jet and they have anhedral...