I found a Brillelli 36cc which went into mine. It fit like a glove! Unfortunately, they went out of business, so you would need to find one used. The carb is side draft, but with the engine mounted inverted, the carb angles downward, maybe 30 degree or so. It is not very obvious. The rest of the engine fit as if the model and engine were engineered together. Cutouts in the cowling lined up with bumps on the engine. Amazing.

I can say to ditch the stock firewall. The lite ply doesn't have enough density to not crush under the strain of a gasser. I would either put some aluminum plating on the back of the stock firewall to support the t-nut and the front, or just make a new one from some aircraft grade plywood. I'm still struggling with mine and dreading trying to get something more to support the upper t-nuts as they are seriously buried at this point.