Drawings from the factory - $100 each. Don't need an STC.
I just did it myself with some aluminum and a fly cutter. As a brand new IA, I submitted a 337 - FSDO should have bounced it back. They just ignored it.
The 337 is one of the most misunderstood and improperly executed documents the government has ever dreamed up.
So I don’t need an stc and factory has instructions !! Thank you !