Im finally starting my performance work this summer, and i wanted to know if anybody knows the ratios on my cars rear gears? It is a 1969 Mach 1 with 351 W and i don't have any tags to id ratios. I was thinking of a 3.50 posi towards the end of my work. Will the 3.50's and posi make a noticeable difference in my power?? Mileage?? Traction??