Doing it by flipping the axles is a lot of unnecessary hastle.. the stock motor isn't timed, and if you are turning this into a crawler, any motor you use wont be timed, so it doesn't mater if it runs forward or backward...
That said, if for some reason you REALLY dont want to switch the wires, what you need to do is take the axles, leave the front in the front and the rear in the rear, but flip each one 180, so the top is the bottom and bottom is top. Remove the axle C's, and swap them end for end so that the steering geometry stays correct, move the upper link mount to the top again, flip the lower link mounts, and move the steering gear to the top.
The part about the C's seems to confuse a lot of people. (if you arent even sure what the axle c is, there is only one part on the axle that looks like the letter C, thats it :lol

if you look at the axle C's, you will notice they are numbered 1 and 2. #1 needs to stay on the right (passenger) side on the front axle, and on the left (driver) side in the rear.
steering linkage is covered in the link above, but its really best to move the axle to the servo, there is way too much slop in the stock system for rock crawling.
(edit) also, the stock upper link mount probably wont just bolt on since its kinda keyed to go on the side its on.... some dremel work may be required... i dont know exactly since i just swapped wires... I would recommend you see if you can get he upper link mounts to work before you do anything else so you dont waste time if you cant make it work.