I found @yukosteel's disassembly of this lens, which helped me get to the focus shims. Those screws holding the focus cam were on TIGHT!
My copy came with 3 identical shims, totaling 0.59mm thick. I removed one, which resulted in extreme back focus instead of the slight front focus. I'm not sure how to get to a final elegant solution, but I've temporarily replaced one of the shims with a couple layers of tape to get a total shim thickness of 0.57mm and perfect focus accuracy wide open. I've been shooting like this for the past few days at various apertures and everything looks sharp! I don't even really notice the focus shift in real world use.
Opening the mount also gave me access to the infinity/minimum focus stop and I decided to test out a way to add a soft stop at ~0.6m, close to where my camera's rangefinder cam decouples from the lens cam. Now I have a tactile indication when I need to switch to live view! This is also still a proof of concept using some gaffer's tape and scotch tape until I come up with a more elegant material/solution, but it's quite satisfying to have the focus ring resistance increase when it reaches the limit of the rangefinder mechanism.
