Looks nice but I don't have good news for You. Length of the DAR-10 was 9,54m with Alfa Romeo 128 R.C.21 engine or 9,83m with Fiat A 74 R.C.38 engine for DAR-10F. That gives 211 (210,76622) and 217 (217,17419) pixels respectively.
And Your drawing is just 204 pixels long (for a longer F model).
Simple method of calculating scale (FD is 22,093 pixels for 1 metre):
size in question in meters x 22,093 = result
And since You're from the USA and still most likely use miles, feets and inches in everyday life, then 1 feet = 0,3048m (or 30,48cm) which means that 1 metre is 3,280839895ft.
There are many conversion tools available in the internet.