@MetroRedLine , thanks, Chris gets the credit for the concept.
If you browse thru the instructions, there are better screw solutions, posted by someone here recently. Smaller Phillips style heads.
The customer’s screw I believe is a Walters 00-90. That head is larger than the countersink on the coupler, which is why I am so interested in the 1.2mm screw.
Unfortunately, I am a transition modeler, but if anyone wants to send similar models to me to design to, I could make as many designs as needed. There are considerations like axle clearance and proper coupler height, but the genetics of the adapter are there to copy and modify.