Wellllll.... first off you go by the wing area and not by the span. Otherwise our "usual" 32 to 36 inch wingspan would produce a design suitable for a .15 engine. So assume that you design the wing to be around 180 to 200 sq inches and go from there. Also something you can do is cheat a little bit. Design the model to come in at around 160 sq inches and then fudge the root and tip chords along with the span a little to keep the "look and feel" but enlarge the area up to 180 to 190 sq inches. You'll need to enlarge the stabilizer a little as well. Likely you'd want to do most of the fudging on the leading edge to push those forward and effectively reduce the long nose moment a little to aid in balancing your creation.

A quick look at an A7E three view shows that for about a 23 inch span which you then fudge up to a 25 to 26 inch span to build up the wing area the fuselage works out to 4 inches tall by 2.5 inchs wide. Now that's obviously wider and taller than you NEED but if you start slimming it down you'll loose a lot of the look that caused the Corsair II to be nicknamed the SLUF. And while it's fairly fat the prop blast will still make it's way around just fine. I wouldn't upset the height as you'll want that for scale recognition and looks in the air. However the width could be fudged a bit to make it down to around 2 to 2 1/4 wide without losing "The Look" too badly.

There's sure no point in makind a big internal duct as the size of that duct will be small enough that the air will stagnate inside and not feed fast enough so it'll act like solid frontal area anyway. This is one spot where the old scale effect really bites us. It's also why EDF models don't do well with designs that have long intake duct lenghts unless a cheater hole is used in the belly to feed more air into the mouth of the fan.

Doing the F8 Vigilante would be one way around this. But while it'll still look good and end up a lot skinnier I think you'll find that a lot of folks won't recognize it and will think you just skinnied up an A7 anyway.