I think technically they want you to have the letter in place before commencing work on the project. I donít see how they would object to receiving the kit before getting the letter in. You will need a serial number, your Vans builder number works.
The letter itself is simple enough, but this the point you declare your planeís gross weight. Changing it later is difficult.
RV-9A #91081, C-GCPT
Dynon SkyView HDX, IO-320 and WW 200RV C/S. Flying as of August 6, 2018