Great work and thanks for sharing all the pictures. So did you ditch the ring gear spacer when you went the custom cap? Will you be selling bits or only completed units?
My interest: I drive a (custom) v8 e36 (with LSD). I want to swap into a e46 but not wanting to loose the LSD. So I already have the e36 diff. I've considered swapping the whole rear assembly (including axles and hubs) with an e46m setup. This has been done on other cars but I'd prefer to stay away from the rare M parts. Will be fall at the earliest I will be making any changes but am enjoying watching the project.
(There were also some can bus issues going to e46 but think I have that solved now.)