Something to point out to everyone following this. The other advantage will be the ability to just order the couplers and springs. This will drive down the cost.
Mario looks good. But would recommend the following
using an cushioned box car to insure length of the draft box .
I don't think your going to get away with out some sort of channel for the coupler similar to the Kadee draft box due to the lug on the bottom of the coupler unless you sand it off.
Also need to redo some measurements. concerning the email. I think I know what your questions are.
Doug