In that case, an RLV R2 pipe is perfect if you are just starting out with a Spec Honda. From my understanding, the R2 has a much broader power band than other Stock Honda pipes, like the R4. Perfect if you are figuring out how to drive the thing.
In the earlier days of Stock Moto, the R2 was THE original, and only legal, pipe for the class. As a result, the R2 is legal at any race you attend, except for the SKUSA events of course (or any race that runs strictly by the book SKUSA rules).
Considering the problem many racers have been having with their R4 pipes cracking, why the governing bodies allowed other pipes besides the R2 in Stock Moto is beyond me. On the other had, adding other pipes besides the R2 is far from the worst parts inclusion the powers-that-be have legalized in this shifter class.