I put a round cowl on my first Hog-Bipe. It had a picture of a radial engine sealed onto a disc of ply with thinned epoxy. The picture disc was glued in to the front of the cowl. One or two "cylinders" were removed to provide engine air. I looked great from the front but kind of klunky from other angles. The box fuselage left giant gaps to the sides and bottom of the cowl.

Now I think to really get a nice radial effect you'd need to make the front of the fuselage round by adding partial formers, stringers, and sheeting. For a lightweight aerobat it seems like a cheeked cowl like for a flat-four type engine would be easier to adapt to the stock fuselage and look better.