Sandpaper should do it.
I mean the pistol grip is held on with a bolt up through the bottom of the grip and a nut dropped through the bottom of the receiver. Shouldn't be any fitment there. Stock has a couple screws, take them out and wiggle it off, wiggle the new one back on. Maybe sand the stock a little to fit.
The lower fore end slides into the receiver and locks in with the latch. That fitment might need sanding on either end.
The upper fore end rotates around the gas tube. There may also need some sanding there. But with upper and lower fore end, I'd try wiggling them to fit first.
Does anyone have any experience replacing the stock pistol grip and fore end on an AK? It looks relatively straight foreword. Some of the parts I've been looking at say may require fitment. I'm pretty handy so I'm trying to find out if I would need any special tools or could I get by with a Dremel and a drill press.