You probably already have your answer.
The Barth WACO builds into a beautiful model. The WACO is an elegant airframe, deserving of a large radial.
Another option may be the Bates Spartan Executive.
http://www.jbplans.com/products-page...5-scale-plans/ But you should check on the cowl diameter. I know that it's large, but I am uncertain of the exact dimmension.
If the Executive is a little small, it would be possible to blow the plans up to a suitable size. The cowl can be built from wood, if desired, so you wouldn't have to worry about parts availability for the non standard size.