Not sure why you would want to purchase a new motor mount support when a dremel can open the area up for you. At TITC in Feb of this year I ran a 48 pitch 66 tooth spur with a 40 tooth pinion which will give a FDR of 3.3. This was the magic FDR for the 13.5 BL Hobbywing system we all used.
To get this to fit I dremeled the top and bottom of the motor support and it was good to go.
On another note since I race my BD7 on low grip netball courts and am still basically using my TITC setup. I am running yok blue springs front and rear, three hole piston, 350 weight Yokomo oil and standard shocks. I am using the 3.5 ff/fr and 2fr/5.7rr toe blocks. I have Tamiya DCJ's up front and yokomo DCJ's on the rear. I am running the plastic c hubs and the remainder of the parts are graphite.(arms, knuckles and rear hubs). I have no issues with handling. The rest of my setup is as meens yokomo setup.
I am currently running blinky 13.5 using the Trinity D3.5 motor and my car i snot much slower than a boosted 17.5.
I am very happy with the car. Tyres I am using Ride 28 blues or reds, when hotter I have been using the 32's.
Comes back to car setup and driving. I forgot to mention I do not have the steering brace fitted and I do not fit screw into the motor support through the top deck.
Just my thoughts,
Later,
Calvin.