It will fit.
It's not easy to get it in there, but it'll go. (Reminds me of rgbeard's sig line
I've had my RC since 2000 and it's been de-armored for cleaning & DWR-ing six or seven times. Twice with replacement pads afterward. They do not need to be cut, the pads are almost exactly the same size as the pockets and the square corners help hold it it place.
Since the hard shell doesn't cover the whole face of the foam, there are corners you can fold in easily to maneuver the pad around the pocket flaps. Then jam your hand in there, straighten the corners out and poke them into the corners of the pocket. This is easiest with the knees and hardest with the elbows.
For the first couple of rides with new pads it seems a little restrictive, but the heat and pressure of your body molds the foam pretty quickly. If/when you remove them after they've molded to your shape, write L & R and an arrow for 'this end in first' on the foam with a sharpie so that when you reinstall them they'll still be shaped right.