Tom,
You are wonderful (even as a charcoal ember).
Good measurements and images.
Here is an image of two 108 mm flanges:
The flange on the left accepts the end-cap but is ‘fine-spline’.
The flange on the right is ‘course-spline’ but won’t accept the end cap.
In fact, I would be concerned about the cage/ball/inner race interference in some cases.
I am not convinced either way that there exists a flange with both course-spline and is compatible with the end cap.
I’m not so much concerned with the roll-pin issue as that can be converted to 6-bolt.
I recall flanges that have the cut-away part to clear balls, etc but I don’t know if an end-cap will fit.
The goal is to figure out how to convert 915s with 100 mm CV joints to 108 mm CV joints.
My personal effort is to additionally use the end cap.
How are you going to address the issue of the gasket if you don’t use the end-cap?
Take a break from CV joints.
Add a log to the fire.
Have an ‘adult beverage’.
Watch the snowflakes.
Think positive Porsche thoughts.
All is well.
Best,
Grady