RE: BP Hobbies 4120 vx Axi 4120
I've found Lucien Miller to be very responsive. I'd suggest mailing him directly. I do own the 4020-16 and it looks the x-mount is 41mm square on centers...
I own two Scorpion motors. Shamefully, they've been sitting for about a year as other things have taken priority. I can say without a doubt, they are of the highest quality in regards to manufacturing and appearance.