The motor mount came from a fellow rc monster poster, his URL is
www.eaglesviewaerial.com/products.html and he does fantastic CNC machining in metal and carbon fiber.
When I first got his mount I installed it as is, with none of the stock REVO motor mounts. There was a ton of chassis flex, so I decide I needed to also use the stock nitro motor mount brackets and reinforcement brace. I had to mill the nitro mount flat so I could bolt the brushless mount on top of it. Then I added the extra Traxxas reinforcement plate and bolted everything together. After all of that there was no flex at all, but I agree that a motor brace (rear or mid) would really bulletproof the mounting. I think I can machine a small "U" shaped bracket that can fit under the motor, which I can bolt to the mount. This should provide good mid/rear mount support for the motor.