Wow, those are my airplanes. A couple of the fiberglass part suppliers offer cowls designed for the Hog-Bipe, I understand they're very similar-looking to the Space Walker cowl. The GreatPlanes cowl is too flimsy to be recommended.
On my previous Hog-Bipe the engine was mounted sideways and a wooden partial cowl was built on. Pretty easy to do and looked "OK", not great.
The thing to do is make the fuselage front round by adding partial formers, stringers, and sheeting, and use a round cowl!!