[RC-Monster Mike]

Changing the front/rear ring and pinion gears isn't an absolute necessity - as long as you have matched your motor, battery, gearing, etc. to the gears you have, you will be fine.
Even though it isn't NECESSARY, I think it is a good idea to use the truggy ratio diffs(if it was my truck, I would use the truggy diffs). The spiral gears are stronger, quieter and smoother, for one. For another, they allow a much smaller spur while retaining a larger pinion, which will be smoother again as well as last longer.