If you look at the pic, you can see a "flat" on the locking lever. If you watch it as you move it, youll see it line up parallel with the face of the rear of the upper hand guard (yours is sloping rearward in the pic, and needs to roll forward). When it does, the hand guard should drop right in place. New or old, its usually a pretty close fit when in the right position.
The problem was that the aftermarket stock was just a tiny bit of a loose fit, and it had some play in how it fitted onto the barrel. The lower handguard was just riding a little high, so once I banged on it a little, the lever swung closed and locked the gas tube into place.
The cleaning rod, on the other hand, was a different story. I had to completely remove the lower handguard to see where the rod was hitting. The frame of the AK has a couple little metal notches that stick up right where the rod has to clear at the last 1/4" to go all the way in. I stuck a thin piece of cardboard in there to act as a ramp, and it went right in.
Thanks to all for the suggestions. From now on, that cleaning rod is staying put.