Yes, L1 + L2 = .707 and L2 = .2
My value for total length should be very accurate, at least within .001". There was no interpolation required to get that value but I had to make a "best guess" for the length of the shoulder portion. I would go with values that give the 10* slope. When I set my dial protractor to that value and held the collet against the arms it appeared to fit perfectly.
If you make one let us know how it works. I'm interested for sure. Just as a note, the factory collets have many slots in them. I was going to count and forgot but I would say it's 6. They work very well as I've never had either of them slip. I've had this router for years and it is the oldest of my collection and might outlive all the newer ones. With no VS or soft start there isn't much that can go wrong with it. I was told when I bought it that it was a 30 year old design that had been well proven to work but I think the lack of features was why it was being discontinued at the time.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.