to ensure the perpendicularity between plane and 4 holes, I tried to mill the plane before making the holes, but it was a test with poor results.The last photo in post #60 shows a milled face on the crank web. What was that operation?
my solution is 4 pins dia 3 mm and a central M4 screw to guarantee the phase for each cylinder and the transmission of the torqueYour Setup with the four Pins is very interesting. It should give a very precise allignement and the screw is only stressed be draw. I used for this connection 4 m3 screws. with no pin the allignement is made with the race of the ball bearing.
The screws are stressed be drwa and maybee also by shearing. So i believe your way is the better solution.