In my heavy Maxx CD Conversion with 1717. I found the MMM does not like the 1717 geared for more than 50mph. You must have a working fan on there and may be better to run it all the time. My fan died and I didnt know and the MMM was actually smoking but still works fine... I think the caps were melting the case?....
In any case I used a Losi CD and used the 50t Truggy spur and a 14t Pinion and the motor was getting seriously close to the outdrive cup. I would go 13-14t and make sure to not get grass in the MMM.

OH BTW MY DIFFS WERE LST SO 13/43 STANDARD BUGGY. NOT SURE ON THE CENS... I think it was 55mph or so...
You can see my thread in my sig...
EDIT. This is what I mean see how close the 1717 is to the cup: