According to published information, I'm pretty sure your numbers are incorrect. Please check the dimensions I layed out made in post #24. With the stock DA standoffs (2-1/2" ), plus the 3/4" provided wood spacer, the distance from the firewall to the prop drive on the DA is 8mm (5/16") more than the same for the 3W with the standoffs and 3/4" wood blocks that QQ used in the prototype shown in the instruction manual. I used 1/2" spacers so that the prop spacing in front of the cowl would virtually identical to the 3W in the manual. The 1/4-5/16"" difference in engine location, on a plane of this size, will have an incredibly minor affect on the CG, given the distance of center of engine mass to the CG location of the plane. MXCop initially flew without a spinner, and I used one. That's a bigger difference.