What prop should I use?

[MADMERCOWNER]

First of all I would really like to thank you guys with helping me with the problems that I had with my outboard. It is running like if it was new. I was ready to junk it and buy a new one. So again thank you very much. You have no idea how much I appreciate the help. Anyway I was wondering if you could tell me what prop I should use. I have a 1976 Mercury 500 50 HP on a 16 foot Peterbourgh. Nothing fancy but I have no idea what I should be using and the prop that is on there now doesn't give much info. It has Michigan stamped on it with these numbers as well 031017. Can anyone help me. My dealer has no clue. It has 13 splines on it.I would like to get some top end out of her. It seems at full throttle she is really screaming and she comes out of the hole really well. So any help would be awsome. Thanx