Another attempt at improving on what is offered commercially.
This is a 35mm prop, 65mm class whoop.
Currently 35mm prop commercial offerings require the use of unique FC boards in a cross pattern, or using a 28.5mm mount spaced curved boards.
The cross pattern boards block some of the swepted prop area.
So you cant use the standard 25.5mm spaced FCs.
Doing some 3d tests seems to show that 35mm props can be accommodated by the standard boards.
So this is a design that does this. In addition it attempts to solve the issue of drag and thrust caused by ductwork.

By replacing the guards with 'rings', duct drag is reduced AND the propeller disc can access air from the front and sides that would otherwise be not provided due to the duct's angle of attack.
The rings minimise airflow disturbance by not being rectangular or square in shape (at some expense in strength).
By having rings, this allows the FC and camera mount to encroach in the space which normally woulve had a duct in it.
By having the right sized rings, theoretically the material used by the duct can be eliminated.

uploaded beefed up version which the 3d printer is estimating to be less than 3 grams.