affas,

I don't have the TF Staggerwing, but it is approximately 1/5.3 scale and the TF 1/5th Dummy Engine can be used. Its trimed to fit size is approximately 8-1/2"(21.5 cm). The Saito 160 twin also fits with in the cowl without cut outs since you did not specify which cylinder (Dummy or actual power plant) location. The cowl gets wider from front to back and at the Dummy Engine location the inside diameter should be approx. 8-1/2" and gets bigger towards the rear.