I assume you're talking about the wrap around grips. I haven't done the wood grips, but I've done a couple of the plastic type of wrap around grips you would find on old Autocockers and such. If I recall correctly I had to shave down the back of the inside of the grip a little where it meets the curved back of the frame. It took about 5 minutes. It's not hard, just common sense.
Edit: Oh yeah, the bottom of the grip will also come down past the frame...if you compare a 'Mag or 'Cocker frame to a Sheridan frame, the former is more square, and the Sheridan rises up at an angle. You'll hardly notice it and it looks clean enough.
If your glasses fog up and you want to make your own mask fans, here's how;
"My happiness doesn't depend on anything. My heart is always happy. I do have anger issues though."