I have a 2.73 open traction rear end. I plan to do some sort of engine work, but I decided to replace my rear end before that. I want to install somewhere between a 3.23 and a 3.73 posi-trac or limited-slip. I am concerned with correctness (if that is a word) of my speedometer. What needs to be done to correct the problem? I have read about the driven/driving gears (i.e. for a 3.23 I will need 17 tooth drive gear and 42 tooth driven gear), but I don't know where they are or where to get the right ones for my rear end swap. Thanks in advance.