In the following pictures I have the XL next to a 88mm long motor and that 88mm long motor next to the 1521.

Neu 1521 is 3.3"/83.82mm long, the XL motors are 2.91"/74mm.

Dude 10s is crazy I had a 8s setup in a Jammin CRT and it was very hard on the diffs my rear ring gears lasted 5-6 charges. I would try Xray diffs I hear they are the best. If you run 10s and make your truck as light as you can. I would suggest 2 5s 4500 30c flightpowers. I have more fun with 5s or 6s setups than I did with my 8s setup it was an expensive lesson to learn. Good luck.

Thanks nl12, that's good advice, I'll definatly consider it as I've gone down the wrong road many times before!

I run 8 Spyder Diffs, do you think they'll be okay? Are the Xrays better than this?

nothing beats the kyosho real harden steel diffs, especialy the tcd up front