It's a standard 1/8 buggy design so it will be the same as many others. How extreme is the center diff offset in the Xray?
Here's the basic options for conversions:
1. motor over the center diff and saddle pack battery... for this you would want to move the diff to the center line of the car. I also moved the diff forward, allowing the battery packs to fit in behind the diff on my 777.
2. motor goes where the rx pack/throttle servo were... battery pack where the nitro motor/pipe were. Like my 8ight....
here's a thread with some pics etc of mine
http://www.rc-monster.com/forum/showthread.php?t=5572
also check out many others here like BrianG's Hyper8 that he's working on for example...