You wont need a new engine..
Your going to need the longer TVPs, the longer dog bones, and if you want the width your going to need to upgrade your diff cups, axles and pick up the extended stub axles.
You could pick everything up for probably right around $40 off of ebay.
I built an XL from pieces and did not see the need for the extended stub axles. However i do have the XL spec axles and diff cups with the standard width stub axles.
Will your upgrading, if you dont already have them, pick up a set of BP diffs and a set of Big Bore shocks from the Flux. The diffs are going to run you about $60-$70
for the pair, and the shocks can be had for about $40.