If I was asked to invert a Schweizer hook I would try and talk whoever wanted it into a Tost hook. If I couldn’t I believe I could use AC 43.13-2B, Chapter 8, paragraph 804 (a), the manufacturers data and other parts of Chapter 8 as appropriate. Field Approvals are kind of hit or miss in my area. In block 8 of the 337 I would start out, “For safety .....”.