You will need:

1 Nitro RS4 of your choice ( I built mine off a RTR, if you have an original Racer, you have most of these parts already)
1 Upright set (part A460*)
2 Suspension Arm sets (part A450*)
1 Turnbuckle Set for NRS4 (part A502**)
2 Rally Sport Shocks Sets (part A771)
Some scrap lexan for shields

It is assumed that you have a minimal working knowledge of your NRS4.  These instructions are here to guid you through the process, not to hold your hand.  If you are relatively new to this, i would suggest having your manual, or the ones available at   http://www.hpiracing.com/instruct.htm handy for refernce.  I will NOT be getting into specific details, but rather will give you an overview of the process.  Read ALL instructions carefully before you begin.  If you do not feel comfortable with ANY portion of this conversion DO NOT BEGIN.  This conversion WILL PERMANENTLY alter your vehicle.

Front End
If you have a NRS42 or  RTR, you will need to swap the front upright set(A461 in these kits), and suspension arms(A453 in these kits) out in favor of parts A460 and A450 respectively.  Refer to the online manuals (any of the pre-RS42 will work) for help in dissasembly/reassembly.  When you install the Hub carriers, remove the part shown in the online Rally manual.  Build the Rally shocks(one set of A771), and install.
For the owners of the NRS4, or NRS4 Racer, simply swap out the existing shocks for the Rally shocks.

Rear End
The chassis on the NRS4 RTR(and i assume all the others) does not allow for the rear suspension arms to travel.  The chassis needs to be notched as shown below. Be SURE that the corners are ROUNED so that they do not create any unnessecary weakness.

Build the second set of Rally Shocks acording to the enclosed instructions, WITH the dirt deflectors.  Swap them for the touring shocks.  The rear suspension arm on the RTR WILL interfere with the rotating of the axle.  Take a dremel and notch the arms where the axles hit them, this will allow the tires to spin freely.

Shielding
The shielding of the drive train is VERY important for this vehicle.  Without proper shielding, your belts and pullies WILL get shredded in offroad use.  My original shielding plans are too complex to form, and some measurments were incorrect.  So I guess you're gonna be on your own for that.  IF I ever get around to re-designing a system that works (and fits) I'll put it up here.

Misc
For offroad work you will need a set of rims, and rally tires.  I would suggest the mesh rims.  The 3 and 5 point rims have large holes which allow twigs etc to get caught.  Also be SURE to get a 3mm (or higher if available) offset rim.  You WILL need the small amount of added stability.
A set of M-Compound rally tires should suffice, but feel free to get what you like.  You will also need to buy a set of foams (or use an extra set you have) as the rally tires do NOT come with any.
I have not yet tested this particular shield configuration, but based on it's design, I can virtually gaurantee thatn you will NOT be getting anything stuck in your belts.  Enjoy.