I have designed this customazible lens cap for various lenses with stepup ring.
The Canon FD caps are for a StepUp ring of the brand "Outlast" with a diameter of 85mm.

You can simply download the Fusion 360 file and enter your data in the fields:

I got the logo as SVG file from the internet and inserted it in Fusion 360.
If you are not familiar with Fusion 360, I can also design or print the lens cap for you.
I printed the first two layers with white "Extrudr PLA NX2" and the remaining layers with “Extrudr FLEX Medium”.
All with 0.2mm layer height.
This makes the lens cap nice and flexible and holds well on the stepup ring.
I hope you find the Lens caps useful! :)
The author hasn't provided the model origin yet.