Well, I wouldn't bother with a Groz. I'd sooner spend some money on an old Stanley. They can be had for little, and can be brought to a high performance level. Some planes just will never amount to much, no matter how much effort you put into them. I haven't used a Groz, but everything I've read about them tells me to go in the other direction. I will respectfully disagree with Mr. DeLaney's second post. You may do some harm to an old Stanley, but at least you have the potential for a fine plane from the get go.
If you're not part of the solution, you're part of the precipitate.