There is a guy fitting a 1717 to a Flux in this project, it is indeed rather difficult:
http://www.beatyourtruck.com/forum/s...x4-E-5SC/page7
For 8s lipo use something with a rather low kv will be needed ideally- not sure if the 1717 is an ideal choice as I seem to recall it having a lower rpm limit than the 15** motors..
Would be worth checking the HPI website to see if the XL has the BP diffs or not- bare in mind there are still guys who manage to kill the BP diffs if they try hard enough so I wouldn't worry so much about that; it is possible to fit ofna & hotbodies 1/8 buggy diffs in the savage so there are always upgrade options.
Hitting up the search feature and checking out other savage-based projects is the best plan really, we have a whole sub-forum dedicated to savage projects as it is..