We have a 91 sunsport and have surfed it. We put a bag in the ski locker. I cant remember how much weight it is but if you contact Wake Makers they can help you with that. I reinforced my ski locker years ago because it was generally weak and cracked. So you'll probably have to do as Michael Hunter suggests. My experience so far with surfing these old boats is 1. It's a PITA filling all those bags manually. Takes my wife and I about 30 mins and we have 3 pumps going at the same time. 2. The bags take up all the room in the boat. Getting the rider in and out is a pain! 3. These boats have WOOD FLOORS AND STRINGERS! As careful as I am, I have had bags do things I didn't expect and have had 8 inches of water in the the back of the boat. ARG!
So, yes it can be done and you can have a great time with a nice wave. No mater what you do, it will never have the wave of a more modern boat and your boat will deteriorate prematurely. Just my 2 cents. Have fun!