That's right, I forgot that 00 was the first year for the V6 Frontier and the H233B came along with it.
As for swapping the shafts from a early 2000 V6 Frontier, odds are it will be a no-brainer. However, there is no way to know if they're 31 or 33 spline shafts other than by inspection. It's not a lot of work to pull them and check, but in a junkyard it might not be much fun. Heck, there might not even be enough room between the truck and the next vehicle to get the shaft out far enough...
The number of them with 31-spline shafts appears to be pretty low too, odds are against you already.

Brent