I believe they are identical. I have a PLR-16, a PLR-22, and an SU-22CA. The same (optional) forend fits both PLR's. The SU-22 comes standard with the forend. This forend interchanges with the one for the pistols. The only difference between the upper receiver/barrel assemblies of the PLR-22 and the SU-22 that I can tell is the overall length of the barrel. Those extra parts in the picture on the Kel-Tec site for the rifle forend must be for installation on an SU-16, and wouldn't be needed on the SU-22.
 
Incidentally, my SU-22 had to go in for a repair, and when it returned, the forend nut was made out of plastic-covered steel, not the plastic-covered aluminum of the past. Anyone else notice this? I know that I prefer the aluminum nut since it is lighter and can't damage the threads on the barrel if I cross thread it.
 
buzzsaw

I could see the plastic covered steel Vs. solid steel being better, the knerling in the steel gets rusty easy but the plastic over the steel is a great idea, i'll keep an eye out for one.