I am in the process of finishing my 2nd Four Star 60. Powered both with an OS 91 FS. In both instances I put the plane together as per the plans. The parts fit together so well that you would have a difficult time changing the placement of the firewall. My 1st Four Star 60 flew just perfect, best flying and easiest flying plane I have ever built. Based on this I would have to assume that whatever thrust is called for is already fixed in the design.